diff mbox series

[v3,13/13] mm/debug_vm_pgtable: populate a pte entry before fetching it

Message ID 20200827080438.315345-14-aneesh.kumar@linux.ibm.com
State New
Headers show
Series mm/debug_vm_pgtable fixes | expand

Commit Message

Aneesh Kumar K.V Aug. 27, 2020, 8:04 a.m. UTC
pte_clear_tests operate on an existing pte entry. Make sure that is not a none
pte entry.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 mm/debug_vm_pgtable.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

kernel test robot Aug. 27, 2020, 12:17 p.m. UTC | #1
Hi "Aneesh,

I love your patch! Perhaps something to improve:

[auto build test WARNING on hnaz-linux-mm/master]
[also build test WARNING on powerpc/next v5.9-rc2 next-20200827]
[cannot apply to mmotm/master]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Aneesh-Kumar-K-V/mm-debug_vm_pgtable-fixes/20200827-160758
base:   https://github.com/hnaz/linux-mm master
config: x86_64-randconfig-s022-20200827 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.2-191-g10164920-dirty
        # save the attached .config to linux build tree
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)

   mm/debug_vm_pgtable.c:509:9: sparse: sparse: incompatible types in conditional expression (different base types):
   mm/debug_vm_pgtable.c:509:9: sparse:    void
   mm/debug_vm_pgtable.c:509:9: sparse:    int
   mm/debug_vm_pgtable.c:528:9: sparse: sparse: incompatible types in conditional expression (different base types):
   mm/debug_vm_pgtable.c:528:9: sparse:    void
   mm/debug_vm_pgtable.c:528:9: sparse:    int
   mm/debug_vm_pgtable.c: note: in included file (through include/linux/pgtable.h, include/linux/mm.h, include/linux/highmem.h):
>> arch/x86/include/asm/pgtable.h:587:27: sparse: sparse: context imbalance in 'debug_vm_pgtable' - unexpected unlock

# https://github.com/0day-ci/linux/commit/9370726f47eaffdf772fdc273d180ec03b245cca
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Aneesh-Kumar-K-V/mm-debug_vm_pgtable-fixes/20200827-160758
git checkout 9370726f47eaffdf772fdc273d180ec03b245cca
vim +/debug_vm_pgtable +587 arch/x86/include/asm/pgtable.h

b534816b552d35 Jeremy Fitzhardinge 2009-02-04  586  
fb43d6cb91ef57 Dave Hansen         2018-04-06 @587  static inline pgprotval_t check_pgprot(pgprot_t pgprot)
fb43d6cb91ef57 Dave Hansen         2018-04-06  588  {
fb43d6cb91ef57 Dave Hansen         2018-04-06  589  	pgprotval_t massaged_val = massage_pgprot(pgprot);
fb43d6cb91ef57 Dave Hansen         2018-04-06  590  
fb43d6cb91ef57 Dave Hansen         2018-04-06  591  	/* mmdebug.h can not be included here because of dependencies */
fb43d6cb91ef57 Dave Hansen         2018-04-06  592  #ifdef CONFIG_DEBUG_VM
fb43d6cb91ef57 Dave Hansen         2018-04-06  593  	WARN_ONCE(pgprot_val(pgprot) != massaged_val,
fb43d6cb91ef57 Dave Hansen         2018-04-06  594  		  "attempted to set unsupported pgprot: %016llx "
fb43d6cb91ef57 Dave Hansen         2018-04-06  595  		  "bits: %016llx supported: %016llx\n",
fb43d6cb91ef57 Dave Hansen         2018-04-06  596  		  (u64)pgprot_val(pgprot),
fb43d6cb91ef57 Dave Hansen         2018-04-06  597  		  (u64)pgprot_val(pgprot) ^ massaged_val,
fb43d6cb91ef57 Dave Hansen         2018-04-06  598  		  (u64)__supported_pte_mask);
fb43d6cb91ef57 Dave Hansen         2018-04-06  599  #endif
fb43d6cb91ef57 Dave Hansen         2018-04-06  600  
fb43d6cb91ef57 Dave Hansen         2018-04-06  601  	return massaged_val;
fb43d6cb91ef57 Dave Hansen         2018-04-06  602  }
fb43d6cb91ef57 Dave Hansen         2018-04-06  603  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
Anshuman Khandual Sept. 1, 2020, 3:25 a.m. UTC | #2
On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
> pte_clear_tests operate on an existing pte entry. Make sure that is not a none
> pte entry.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  mm/debug_vm_pgtable.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 21329c7d672f..8527ebb75f2c 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>  static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>  				   unsigned long vaddr)
>  {
> -	pte_t pte = ptep_get(ptep);
> +	pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep);

Seems like ptep_get_and_clear() here just clears the entry in preparation
for a following set_pte_at() which otherwise would have been a problem on
ppc64 as you had pointed out earlier i.e set_pte_at() should not update an
existing valid entry. So the commit message here is bit misleading.

>  
>  	pr_debug("Validating PTE clear\n");
>  	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
> @@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void)
>  	p4d_t *p4dp, *saved_p4dp;
>  	pud_t *pudp, *saved_pudp;
>  	pmd_t *pmdp, *saved_pmdp, pmd;
> -	pte_t *ptep;
> +	pte_t *ptep, pte;
>  	pgtable_t saved_ptep;
>  	pgprot_t prot, protnone;
>  	phys_addr_t paddr;
> @@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void)
>  	 */
>  
>  	ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
> +	pte = pfn_pte(pte_aligned, prot);
> +	set_pte_at(mm, vaddr, ptep, pte);

Not here, creating and populating an entry must be done in respective
test functions itself. Besides, this seems bit redundant as well. The
test pte_clear_tests() with the above change added, already

- Clears the PTEP entry with ptep_get_and_clear()
- Creates and populates the PTEP with set_pte_at()
- Clears with pte_clear()
- Checks for pte_none()

If the objective is to clear the PTEP entry before calling set_pte_at(),
then only the first chunk is required and it should also be merged with
a previous patch. 

[PATCH v3 07/13] mm/debug_vm_pgtable/set_pte/pmd/pud: Don't use set_*_at to update an existing pte entry 


>  	pte_clear_tests(mm, ptep, vaddr);
>  	pte_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>  	pte_unmap_unlock(ptep, ptl);
> 

There is a checkpatch.pl warning here.

WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#7: 
pte_clear_tests operate on an existing pte entry. Make sure that is not a none

total: 0 errors, 1 warnings, 24 lines checked

There is also a build failure on x86 reported from kernel test robot.
Aneesh Kumar K.V Sept. 1, 2020, 6:37 a.m. UTC | #3
On 9/1/20 8:55 AM, Anshuman Khandual wrote:
> 
> 
> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
>> pte_clear_tests operate on an existing pte entry. Make sure that is not a none
>> pte entry.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>   mm/debug_vm_pgtable.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index 21329c7d672f..8527ebb75f2c 100644
>> --- a/mm/debug_vm_pgtable.c
>> +++ b/mm/debug_vm_pgtable.c
>> @@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>>   static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>>   				   unsigned long vaddr)
>>   {
>> -	pte_t pte = ptep_get(ptep);
>> +	pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep);
> 
> Seems like ptep_get_and_clear() here just clears the entry in preparation
> for a following set_pte_at() which otherwise would have been a problem on
> ppc64 as you had pointed out earlier i.e set_pte_at() should not update an
> existing valid entry. So the commit message here is bit misleading.
> 

and also fetch the pte value which is used further.


>>   
>>   	pr_debug("Validating PTE clear\n");
>>   	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>> @@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void)
>>   	p4d_t *p4dp, *saved_p4dp;
>>   	pud_t *pudp, *saved_pudp;
>>   	pmd_t *pmdp, *saved_pmdp, pmd;
>> -	pte_t *ptep;
>> +	pte_t *ptep, pte;
>>   	pgtable_t saved_ptep;
>>   	pgprot_t prot, protnone;
>>   	phys_addr_t paddr;
>> @@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void)
>>   	 */
>>   
>>   	ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>> +	pte = pfn_pte(pte_aligned, prot);
>> +	set_pte_at(mm, vaddr, ptep, pte);
> 
> Not here, creating and populating an entry must be done in respective
> test functions itself. Besides, this seems bit redundant as well. The
> test pte_clear_tests() with the above change added, already
> 
> - Clears the PTEP entry with ptep_get_and_clear()

and fetch the old value set previously.

> - Creates and populates the PTEP with set_pte_at()
> - Clears with pte_clear()
> - Checks for pte_none()
> 
> If the objective is to clear the PTEP entry before calling set_pte_at(),
> then only the first chunk is required and it should also be merged with
> a previous patch.
> 
> [PATCH v3 07/13] mm/debug_vm_pgtable/set_pte/pmd/pud: Don't use set_*_at to update an existing pte entry
> 
> 
>>   	pte_clear_tests(mm, ptep, vaddr);
>>   	pte_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>>   	pte_unmap_unlock(ptep, ptl);
>>
> 
> There is a checkpatch.pl warning here.
> 
> WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
> #7:
> pte_clear_tests operate on an existing pte entry. Make sure that is not a none
> 
> total: 0 errors, 1 warnings, 24 lines checked
> 
> There is also a build failure on x86 reported from kernel test robot.
>
Anshuman Khandual Sept. 1, 2020, 7:38 a.m. UTC | #4
On 09/01/2020 12:07 PM, Aneesh Kumar K.V wrote:
> On 9/1/20 8:55 AM, Anshuman Khandual wrote:
>>
>>
>> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
>>> pte_clear_tests operate on an existing pte entry. Make sure that is not a none
>>> pte entry.
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>> ---
>>>   mm/debug_vm_pgtable.c | 6 ++++--
>>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>> index 21329c7d672f..8527ebb75f2c 100644
>>> --- a/mm/debug_vm_pgtable.c
>>> +++ b/mm/debug_vm_pgtable.c
>>> @@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>>>   static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>>>                      unsigned long vaddr)
>>>   {
>>> -    pte_t pte = ptep_get(ptep);
>>> +    pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep);
>>
>> Seems like ptep_get_and_clear() here just clears the entry in preparation
>> for a following set_pte_at() which otherwise would have been a problem on
>> ppc64 as you had pointed out earlier i.e set_pte_at() should not update an
>> existing valid entry. So the commit message here is bit misleading.
>>
> 
> and also fetch the pte value which is used further.
> 
> 
>>>         pr_debug("Validating PTE clear\n");
>>>       pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>>> @@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void)
>>>       p4d_t *p4dp, *saved_p4dp;
>>>       pud_t *pudp, *saved_pudp;
>>>       pmd_t *pmdp, *saved_pmdp, pmd;
>>> -    pte_t *ptep;
>>> +    pte_t *ptep, pte;
>>>       pgtable_t saved_ptep;
>>>       pgprot_t prot, protnone;
>>>       phys_addr_t paddr;
>>> @@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void)
>>>        */
>>>         ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>>> +    pte = pfn_pte(pte_aligned, prot);
>>> +    set_pte_at(mm, vaddr, ptep, pte);
>>
>> Not here, creating and populating an entry must be done in respective
>> test functions itself. Besides, this seems bit redundant as well. The
>> test pte_clear_tests() with the above change added, already
>>
>> - Clears the PTEP entry with ptep_get_and_clear()
> 
> and fetch the old value set previously.

In that case, please move above two lines i.e

pte = pfn_pte(pte_aligned, prot);
set_pte_at(mm, vaddr, ptep, pte);

from debug_vm_pgtable() to pte_clear_tests() and update it's arguments
as required.
Aneesh Kumar K.V Sept. 1, 2020, 9:58 a.m. UTC | #5
On 9/1/20 1:08 PM, Anshuman Khandual wrote:
> 
> 
> On 09/01/2020 12:07 PM, Aneesh Kumar K.V wrote:
>> On 9/1/20 8:55 AM, Anshuman Khandual wrote:
>>>
>>>
>>> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
>>>> pte_clear_tests operate on an existing pte entry. Make sure that is not a none
>>>> pte entry.
>>>>
>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>>> ---
>>>>    mm/debug_vm_pgtable.c | 6 ++++--
>>>>    1 file changed, 4 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>>> index 21329c7d672f..8527ebb75f2c 100644
>>>> --- a/mm/debug_vm_pgtable.c
>>>> +++ b/mm/debug_vm_pgtable.c
>>>> @@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>>>>    static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>>>>                       unsigned long vaddr)
>>>>    {
>>>> -    pte_t pte = ptep_get(ptep);
>>>> +    pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep);
>>>
>>> Seems like ptep_get_and_clear() here just clears the entry in preparation
>>> for a following set_pte_at() which otherwise would have been a problem on
>>> ppc64 as you had pointed out earlier i.e set_pte_at() should not update an
>>> existing valid entry. So the commit message here is bit misleading.
>>>
>>
>> and also fetch the pte value which is used further.
>>
>>
>>>>          pr_debug("Validating PTE clear\n");
>>>>        pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>>>> @@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void)
>>>>        p4d_t *p4dp, *saved_p4dp;
>>>>        pud_t *pudp, *saved_pudp;
>>>>        pmd_t *pmdp, *saved_pmdp, pmd;
>>>> -    pte_t *ptep;
>>>> +    pte_t *ptep, pte;
>>>>        pgtable_t saved_ptep;
>>>>        pgprot_t prot, protnone;
>>>>        phys_addr_t paddr;
>>>> @@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void)
>>>>         */
>>>>          ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>>>> +    pte = pfn_pte(pte_aligned, prot);
>>>> +    set_pte_at(mm, vaddr, ptep, pte);
>>>
>>> Not here, creating and populating an entry must be done in respective
>>> test functions itself. Besides, this seems bit redundant as well. The
>>> test pte_clear_tests() with the above change added, already
>>>
>>> - Clears the PTEP entry with ptep_get_and_clear()
>>
>> and fetch the old value set previously.
> 
> In that case, please move above two lines i.e
> 
> pte = pfn_pte(pte_aligned, prot);
> set_pte_at(mm, vaddr, ptep, pte);
> 
> from debug_vm_pgtable() to pte_clear_tests() and update it's arguments
> as required.
> 

Frankly, I don't understand what these tests are testing. It all looks 
like some random clear and set.

static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
				   unsigned long vaddr, unsigned long pfn,
				   pgprot_t prot)
{

	pte_t pte = pfn_pte(pfn, prot);
	set_pte_at(mm, vaddr, ptep, pte);

	pte =  ptep_get_and_clear(mm, vaddr, ptep);

	pr_debug("Validating PTE clear\n");
	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
	set_pte_at(mm, vaddr, ptep, pte);
	barrier();
	pte_clear(mm, vaddr, ptep);
	pte = ptep_get(ptep);
	WARN_ON(!pte_none(pte));
}


-aneesh
Anshuman Khandual Sept. 2, 2020, 3:49 a.m. UTC | #6
On 09/01/2020 03:28 PM, Aneesh Kumar K.V wrote:
> On 9/1/20 1:08 PM, Anshuman Khandual wrote:
>>
>>
>> On 09/01/2020 12:07 PM, Aneesh Kumar K.V wrote:
>>> On 9/1/20 8:55 AM, Anshuman Khandual wrote:
>>>>
>>>>
>>>> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
>>>>> pte_clear_tests operate on an existing pte entry. Make sure that is not a none
>>>>> pte entry.
>>>>>
>>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>>>> ---
>>>>>    mm/debug_vm_pgtable.c | 6 ++++--
>>>>>    1 file changed, 4 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>>>> index 21329c7d672f..8527ebb75f2c 100644
>>>>> --- a/mm/debug_vm_pgtable.c
>>>>> +++ b/mm/debug_vm_pgtable.c
>>>>> @@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>>>>>    static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>>>>>                       unsigned long vaddr)
>>>>>    {
>>>>> -    pte_t pte = ptep_get(ptep);
>>>>> +    pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep);
>>>>
>>>> Seems like ptep_get_and_clear() here just clears the entry in preparation
>>>> for a following set_pte_at() which otherwise would have been a problem on
>>>> ppc64 as you had pointed out earlier i.e set_pte_at() should not update an
>>>> existing valid entry. So the commit message here is bit misleading.
>>>>
>>>
>>> and also fetch the pte value which is used further.
>>>
>>>
>>>>>          pr_debug("Validating PTE clear\n");
>>>>>        pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>>>>> @@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void)
>>>>>        p4d_t *p4dp, *saved_p4dp;
>>>>>        pud_t *pudp, *saved_pudp;
>>>>>        pmd_t *pmdp, *saved_pmdp, pmd;
>>>>> -    pte_t *ptep;
>>>>> +    pte_t *ptep, pte;
>>>>>        pgtable_t saved_ptep;
>>>>>        pgprot_t prot, protnone;
>>>>>        phys_addr_t paddr;
>>>>> @@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void)
>>>>>         */
>>>>>          ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>>>>> +    pte = pfn_pte(pte_aligned, prot);
>>>>> +    set_pte_at(mm, vaddr, ptep, pte);
>>>>
>>>> Not here, creating and populating an entry must be done in respective
>>>> test functions itself. Besides, this seems bit redundant as well. The
>>>> test pte_clear_tests() with the above change added, already
>>>>
>>>> - Clears the PTEP entry with ptep_get_and_clear()
>>>
>>> and fetch the old value set previously.
>>
>> In that case, please move above two lines i.e
>>
>> pte = pfn_pte(pte_aligned, prot);
>> set_pte_at(mm, vaddr, ptep, pte);
>>
>> from debug_vm_pgtable() to pte_clear_tests() and update it's arguments
>> as required.
>>
> 
> Frankly, I don't understand what these tests are testing. It all looks like some random clear and set.

The idea here is to have some value with some randomness preferably, in
a given PTEP before attempting to clear the entry, in order to make sure
that pte_clear() is indeed clearing something of non-zero value.

> 
> static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>                    unsigned long vaddr, unsigned long pfn,
>                    pgprot_t prot)
> {
> 
>     pte_t pte = pfn_pte(pfn, prot);
>     set_pte_at(mm, vaddr, ptep, pte);
> 
>     pte =  ptep_get_and_clear(mm, vaddr, ptep);

Looking at this again, this preceding pfn_pte() followed by set_pte_at()
is not really required. Its reasonable to start with what ever was there
in the PTEP as a seed value which anyway gets added with RANDOM_ORVALUE.
s/ptep_get/ptep_get_and_clear is sufficient to take care of the powerpc
set_pte_at() constraint.
Aneesh Kumar K.V Sept. 2, 2020, 3:58 a.m. UTC | #7
On 9/2/20 9:19 AM, Anshuman Khandual wrote:
> 
> 
> On 09/01/2020 03:28 PM, Aneesh Kumar K.V wrote:
>> On 9/1/20 1:08 PM, Anshuman Khandual wrote:
>>>
>>>
>>> On 09/01/2020 12:07 PM, Aneesh Kumar K.V wrote:
>>>> On 9/1/20 8:55 AM, Anshuman Khandual wrote:
>>>>>
>>>>>
>>>>> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
>>>>>> pte_clear_tests operate on an existing pte entry. Make sure that is not a none
>>>>>> pte entry.
>>>>>>
>>>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>>>>> ---
>>>>>>     mm/debug_vm_pgtable.c | 6 ++++--
>>>>>>     1 file changed, 4 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>>>>> index 21329c7d672f..8527ebb75f2c 100644
>>>>>> --- a/mm/debug_vm_pgtable.c
>>>>>> +++ b/mm/debug_vm_pgtable.c
>>>>>> @@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
>>>>>>     static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>>>>>>                        unsigned long vaddr)
>>>>>>     {
>>>>>> -    pte_t pte = ptep_get(ptep);
>>>>>> +    pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep);
>>>>>
>>>>> Seems like ptep_get_and_clear() here just clears the entry in preparation
>>>>> for a following set_pte_at() which otherwise would have been a problem on
>>>>> ppc64 as you had pointed out earlier i.e set_pte_at() should not update an
>>>>> existing valid entry. So the commit message here is bit misleading.
>>>>>
>>>>
>>>> and also fetch the pte value which is used further.
>>>>
>>>>
>>>>>>           pr_debug("Validating PTE clear\n");
>>>>>>         pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>>>>>> @@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void)
>>>>>>         p4d_t *p4dp, *saved_p4dp;
>>>>>>         pud_t *pudp, *saved_pudp;
>>>>>>         pmd_t *pmdp, *saved_pmdp, pmd;
>>>>>> -    pte_t *ptep;
>>>>>> +    pte_t *ptep, pte;
>>>>>>         pgtable_t saved_ptep;
>>>>>>         pgprot_t prot, protnone;
>>>>>>         phys_addr_t paddr;
>>>>>> @@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void)
>>>>>>          */
>>>>>>           ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>>>>>> +    pte = pfn_pte(pte_aligned, prot);
>>>>>> +    set_pte_at(mm, vaddr, ptep, pte);
>>>>>
>>>>> Not here, creating and populating an entry must be done in respective
>>>>> test functions itself. Besides, this seems bit redundant as well. The
>>>>> test pte_clear_tests() with the above change added, already
>>>>>
>>>>> - Clears the PTEP entry with ptep_get_and_clear()
>>>>
>>>> and fetch the old value set previously.
>>>
>>> In that case, please move above two lines i.e
>>>
>>> pte = pfn_pte(pte_aligned, prot);
>>> set_pte_at(mm, vaddr, ptep, pte);
>>>
>>> from debug_vm_pgtable() to pte_clear_tests() and update it's arguments
>>> as required.
>>>
>>
>> Frankly, I don't understand what these tests are testing. It all looks like some random clear and set.
> 
> The idea here is to have some value with some randomness preferably, in
> a given PTEP before attempting to clear the entry, in order to make sure
> that pte_clear() is indeed clearing something of non-zero value.
> 
>>
>> static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
>>                     unsigned long vaddr, unsigned long pfn,
>>                     pgprot_t prot)
>> {
>>
>>      pte_t pte = pfn_pte(pfn, prot);
>>      set_pte_at(mm, vaddr, ptep, pte);
>>
>>      pte =  ptep_get_and_clear(mm, vaddr, ptep);
> 
> Looking at this again, this preceding pfn_pte() followed by set_pte_at()
> is not really required. Its reasonable to start with what ever was there
> in the PTEP as a seed value which anyway gets added with RANDOM_ORVALUE.
> s/ptep_get/ptep_get_and_clear is sufficient to take care of the powerpc
> set_pte_at() constraint.
> 

But the way test is written we had none pte before. That is why I added 
that set_pte_at to put something there. With none pte the below sequence 
fails.

	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
	set_pte_at(mm, vaddr, ptep, pte);


because nobody is marking a _PAGE_PTE there.

	pte_t pte = pfn_pte(pfn, prot);

	pr_debug("Validating PTE clear\n");
	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
	set_pte_at(mm, vaddr, ptep, pte);
	barrier();
	pte_clear(mm, vaddr, ptep);
	pte = ptep_get(ptep);
	WARN_ON(!pte_none(pte));

will that work for you?

-aneesh
diff mbox series

Patch

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 21329c7d672f..8527ebb75f2c 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -546,7 +546,7 @@  static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
 static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
 				   unsigned long vaddr)
 {
-	pte_t pte = ptep_get(ptep);
+	pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep);
 
 	pr_debug("Validating PTE clear\n");
 	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
@@ -944,7 +944,7 @@  static int __init debug_vm_pgtable(void)
 	p4d_t *p4dp, *saved_p4dp;
 	pud_t *pudp, *saved_pudp;
 	pmd_t *pmdp, *saved_pmdp, pmd;
-	pte_t *ptep;
+	pte_t *ptep, pte;
 	pgtable_t saved_ptep;
 	pgprot_t prot, protnone;
 	phys_addr_t paddr;
@@ -1049,6 +1049,8 @@  static int __init debug_vm_pgtable(void)
 	 */
 
 	ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
+	pte = pfn_pte(pte_aligned, prot);
+	set_pte_at(mm, vaddr, ptep, pte);
 	pte_clear_tests(mm, ptep, vaddr);
 	pte_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
 	pte_unmap_unlock(ptep, ptl);