[kernel,3/4] powerpc/mm/iommu: Make mm_iommu_new() fail on existing regions

Message ID 20181015092416.47380-4-aik@ozlabs.ru
State New
Headers show
Series
  • vfio/spapr_tce: Reworks for NVIDIA V100 + P9 passthrough (part 1)
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Commit Message

Alexey Kardashevskiy Oct. 15, 2018, 9:24 a.m.
Since we are going to have 2 different preregistering helpers, let's
make it clear that mm_iommu_new() is only for the normal (i.e. not device)
memory and for existing areas mm_iommu_get() should be used instead.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 arch/powerpc/mm/mmu_context_iommu.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Comments

David Gibson Oct. 17, 2018, 1 a.m. | #1
On Mon, Oct 15, 2018 at 08:24:15PM +1100, Alexey Kardashevskiy wrote:
> Since we are going to have 2 different preregistering helpers, let's
> make it clear that mm_iommu_new() is only for the normal (i.e. not device)
> memory and for existing areas mm_iommu_get() should be used instead.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

I think the idea is sensible.  However (and, yes, this is really an
existing bug) - shouldn't we check for a request to add anything
overlapping with an existing region, not just one that exactly
matches?

> ---
>  arch/powerpc/mm/mmu_context_iommu.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
> index a8c4a3c..839dbce 100644
> --- a/arch/powerpc/mm/mmu_context_iommu.c
> +++ b/arch/powerpc/mm/mmu_context_iommu.c
> @@ -141,8 +141,7 @@ long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list,
>  			next) {
>  		if ((mem->ua == ua) && (mem->entries == entries)) {
> -			++mem->used;
> -			*pmem = mem;
> +			ret = -EBUSY;
>  			goto unlock_exit;
>  		}
>
Alexey Kardashevskiy Oct. 17, 2018, 3:34 a.m. | #2
On 17/10/2018 12:00, David Gibson wrote:
> On Mon, Oct 15, 2018 at 08:24:15PM +1100, Alexey Kardashevskiy wrote:
>> Since we are going to have 2 different preregistering helpers, let's
>> make it clear that mm_iommu_new() is only for the normal (i.e. not device)
>> memory and for existing areas mm_iommu_get() should be used instead.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> 
> I think the idea is sensible.  However (and, yes, this is really an
> existing bug) - shouldn't we check for a request to add anything
> overlapping with an existing region, not just one that exactly
> matches?

The overlap check is below the changed hunk:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/mm/mmu_context_iommu.c#n150


> 
>> ---
>>  arch/powerpc/mm/mmu_context_iommu.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
>> index a8c4a3c..839dbce 100644
>> --- a/arch/powerpc/mm/mmu_context_iommu.c
>> +++ b/arch/powerpc/mm/mmu_context_iommu.c
>> @@ -141,8 +141,7 @@ long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>>  	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list,
>>  			next) {
>>  		if ((mem->ua == ua) && (mem->entries == entries)) {
>> -			++mem->used;
>> -			*pmem = mem;
>> +			ret = -EBUSY;
>>  			goto unlock_exit;
>>  		}
>>  
>
David Gibson Oct. 17, 2018, 4:45 a.m. | #3
On Wed, Oct 17, 2018 at 02:34:32PM +1100, Alexey Kardashevskiy wrote:
> 
> 
> On 17/10/2018 12:00, David Gibson wrote:
> > On Mon, Oct 15, 2018 at 08:24:15PM +1100, Alexey Kardashevskiy wrote:
> >> Since we are going to have 2 different preregistering helpers, let's
> >> make it clear that mm_iommu_new() is only for the normal (i.e. not device)
> >> memory and for existing areas mm_iommu_get() should be used instead.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> > 
> > I think the idea is sensible.  However (and, yes, this is really an
> > existing bug) - shouldn't we check for a request to add anything
> > overlapping with an existing region, not just one that exactly
> > matches?
> 
> The overlap check is below the changed hunk:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/mm/mmu_context_iommu.c#n150

Ah, right.

In that case can't you just drop this whole if.  I don't see that
there's any use in giving different error codes for "tried to register
exactly a region you registered before" and "tried to register a
region overlapping one you registered before.


> 
> 
> > 
> >> ---
> >>  arch/powerpc/mm/mmu_context_iommu.c | 3 +--
> >>  1 file changed, 1 insertion(+), 2 deletions(-)
> >>
> >> diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
> >> index a8c4a3c..839dbce 100644
> >> --- a/arch/powerpc/mm/mmu_context_iommu.c
> >> +++ b/arch/powerpc/mm/mmu_context_iommu.c
> >> @@ -141,8 +141,7 @@ long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
> >>  	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list,
> >>  			next) {
> >>  		if ((mem->ua == ua) && (mem->entries == entries)) {
> >> -			++mem->used;
> >> -			*pmem = mem;
> >> +			ret = -EBUSY;
> >>  			goto unlock_exit;
> >>  		}
> >>  
> > 
>

Patch

diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
index a8c4a3c..839dbce 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -141,8 +141,7 @@  long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
 	list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list,
 			next) {
 		if ((mem->ua == ua) && (mem->entries == entries)) {
-			++mem->used;
-			*pmem = mem;
+			ret = -EBUSY;
 			goto unlock_exit;
 		}