| Message ID | 1503007519-26777-21-git-send-email-ldufour@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
On 08/18/2017 03:35 AM, Laurent Dufour wrote: > This patch enable the speculative page fault on the PowerPC > architecture. > > This will try a speculative page fault without holding the mmap_sem, > if it returns with WM_FAULT_RETRY, the mmap_sem is acquired and the s/WM_FAULT_RETRY/VM_FAULT_RETRY/ > traditional page fault processing is done. > > Support is only provide for BOOK3S_64 currently because: > - require CONFIG_PPC_STD_MMU because checks done in > set_access_flags_filter() What checks are done in set_access_flags_filter() ? We are just adding the code block in do_page_fault(). > - require BOOK3S because we can't support for book3e_hugetlb_preload() > called by update_mmu_cache() > > Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com> > --- > arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++++ > arch/powerpc/mm/fault.c | 30 +++++++++++++++++++++++++++- > 2 files changed, 34 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h > index 818a58fc3f4f..897f8b9f67e6 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -313,6 +313,11 @@ extern unsigned long pci_io_base; > /* Advertise support for _PAGE_SPECIAL */ > #define __HAVE_ARCH_PTE_SPECIAL > > +/* Advertise that we call the Speculative Page Fault handler */ > +#if defined(CONFIG_PPC_BOOK3S_64) > +#define __HAVE_ARCH_CALL_SPF > +#endif > + > #ifndef __ASSEMBLY__ > > /* > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c > index 4c422632047b..7b3cc4c30eab 100644 > --- a/arch/powerpc/mm/fault.c > +++ b/arch/powerpc/mm/fault.c > @@ -291,9 +291,36 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, > if (is_write && is_user) > store_update_sp = store_updates_sp(regs); > > - if (is_user) > + if (is_user) { > flags |= FAULT_FLAG_USER; > > +#if defined(__HAVE_ARCH_CALL_SPF) > + /* let's try a speculative page fault without grabbing the > + * mmap_sem. > + */ > + > + /* > + * flags is set later based on the VMA's flags, for the common > + * speculative service, we need some flags to be set. > + */ > + if (is_write) > + flags |= FAULT_FLAG_WRITE; > + > + fault = handle_speculative_fault(mm, address, flags); > + if (!(fault & VM_FAULT_RETRY || fault & VM_FAULT_ERROR)) { > + perf_sw_event(PERF_COUNT_SW_SPF_DONE, 1, > + regs, address); > + goto done; Why we should retry with classical page fault on VM_FAULT_ERROR ? We should always return VM_FAULT_RETRY in case there is a clear collision some where which requires retry with classical method and return VM_FAULT_ERROR in cases where we know that it cannot be retried and fail for good. Should not handle_speculative_fault() be changed to accommodate this ? > + } > + > + /* > + * Resetting flags since the following code assumes > + * FAULT_FLAG_WRITE is not set. > + */ > + flags &= ~FAULT_FLAG_WRITE; > +#endif /* defined(__HAVE_ARCH_CALL_SPF) */ Setting and resetting of FAULT_FLAG_WRITE seems confusing. Why you say that some flags need to be set for handle_speculative_fault() function. Could you elaborate on this ?
On 21/08/2017 08:58, Anshuman Khandual wrote: > On 08/18/2017 03:35 AM, Laurent Dufour wrote: >> This patch enable the speculative page fault on the PowerPC >> architecture. >> >> This will try a speculative page fault without holding the mmap_sem, >> if it returns with WM_FAULT_RETRY, the mmap_sem is acquired and the > > s/WM_FAULT_RETRY/VM_FAULT_RETRY/ Good catch ;) >> traditional page fault processing is done. >> >> Support is only provide for BOOK3S_64 currently because: >> - require CONFIG_PPC_STD_MMU because checks done in >> set_access_flags_filter() > > What checks are done in set_access_flags_filter() ? We are just > adding the code block in do_page_fault(). set_access_flags_filter() is checking for vm_flags & VM_EXEC which may be changed in our back, leading to a spurious WARN displayed. This being said, I focused on the BOOK3S as this meaningful for large system, and I didn't get time to check for embedded systems. > >> - require BOOK3S because we can't support for book3e_hugetlb_preload() >> called by update_mmu_cache() >> >> Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com> >> --- >> arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++++ >> arch/powerpc/mm/fault.c | 30 +++++++++++++++++++++++++++- >> 2 files changed, 34 insertions(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h >> index 818a58fc3f4f..897f8b9f67e6 100644 >> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h >> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h >> @@ -313,6 +313,11 @@ extern unsigned long pci_io_base; >> /* Advertise support for _PAGE_SPECIAL */ >> #define __HAVE_ARCH_PTE_SPECIAL >> >> +/* Advertise that we call the Speculative Page Fault handler */ >> +#if defined(CONFIG_PPC_BOOK3S_64) >> +#define __HAVE_ARCH_CALL_SPF >> +#endif >> + >> #ifndef __ASSEMBLY__ >> >> /* >> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c >> index 4c422632047b..7b3cc4c30eab 100644 >> --- a/arch/powerpc/mm/fault.c >> +++ b/arch/powerpc/mm/fault.c >> @@ -291,9 +291,36 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, >> if (is_write && is_user) >> store_update_sp = store_updates_sp(regs); >> >> - if (is_user) >> + if (is_user) { >> flags |= FAULT_FLAG_USER; >> >> +#if defined(__HAVE_ARCH_CALL_SPF) >> + /* let's try a speculative page fault without grabbing the >> + * mmap_sem. >> + */ >> + >> + /* >> + * flags is set later based on the VMA's flags, for the common >> + * speculative service, we need some flags to be set. >> + */ >> + if (is_write) >> + flags |= FAULT_FLAG_WRITE; >> + >> + fault = handle_speculative_fault(mm, address, flags); >> + if (!(fault & VM_FAULT_RETRY || fault & VM_FAULT_ERROR)) { >> + perf_sw_event(PERF_COUNT_SW_SPF_DONE, 1, >> + regs, address); >> + goto done; > > Why we should retry with classical page fault on VM_FAULT_ERROR ? > We should always return VM_FAULT_RETRY in case there is a clear > collision some where which requires retry with classical method > and return VM_FAULT_ERROR in cases where we know that it cannot > be retried and fail for good. Should not handle_speculative_fault() > be changed to accommodate this ? There is no need to change handle_speculative_fault(), it should return VM_FAULT_RETRY when a retry is required. If VM_FAULT_ERROR is return, we should be able to jump to the block dealing with VM_FAULT_ERROR and calling vm_fault_error(). > >> + } >> + >> + /* >> + * Resetting flags since the following code assumes >> + * FAULT_FLAG_WRITE is not set. >> + */ >> + flags &= ~FAULT_FLAG_WRITE; >> +#endif /* defined(__HAVE_ARCH_CALL_SPF) */ > > Setting and resetting of FAULT_FLAG_WRITE seems confusing. Why you > say that some flags need to be set for handle_speculative_fault() > function. Could you elaborate on this ? FAULT_FLAG_WRITE is required to handle write access. In the case we retry with the classical path, the flag is reset and will be set later if !is_exec and is_write.
diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h index 818a58fc3f4f..897f8b9f67e6 100644 --- a/arch/powerpc/include/asm/book3s/64/pgtable.h +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h @@ -313,6 +313,11 @@ extern unsigned long pci_io_base; /* Advertise support for _PAGE_SPECIAL */ #define __HAVE_ARCH_PTE_SPECIAL +/* Advertise that we call the Speculative Page Fault handler */ +#if defined(CONFIG_PPC_BOOK3S_64) +#define __HAVE_ARCH_CALL_SPF +#endif + #ifndef __ASSEMBLY__ /* diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index 4c422632047b..7b3cc4c30eab 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -291,9 +291,36 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, if (is_write && is_user) store_update_sp = store_updates_sp(regs); - if (is_user) + if (is_user) { flags |= FAULT_FLAG_USER; +#if defined(__HAVE_ARCH_CALL_SPF) + /* let's try a speculative page fault without grabbing the + * mmap_sem. + */ + + /* + * flags is set later based on the VMA's flags, for the common + * speculative service, we need some flags to be set. + */ + if (is_write) + flags |= FAULT_FLAG_WRITE; + + fault = handle_speculative_fault(mm, address, flags); + if (!(fault & VM_FAULT_RETRY || fault & VM_FAULT_ERROR)) { + perf_sw_event(PERF_COUNT_SW_SPF_DONE, 1, + regs, address); + goto done; + } + + /* + * Resetting flags since the following code assumes + * FAULT_FLAG_WRITE is not set. + */ + flags &= ~FAULT_FLAG_WRITE; +#endif /* defined(__HAVE_ARCH_CALL_SPF) */ + } + /* When running in the kernel we expect faults to occur only to * addresses in user space. All other faults represent errors in the * kernel and should generate an OOPS. Unfortunately, in the case of an @@ -479,6 +506,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, rc = 0; } +done: /* * Major/minor page fault accounting. */
This patch enable the speculative page fault on the PowerPC architecture. This will try a speculative page fault without holding the mmap_sem, if it returns with WM_FAULT_RETRY, the mmap_sem is acquired and the traditional page fault processing is done. Support is only provide for BOOK3S_64 currently because: - require CONFIG_PPC_STD_MMU because checks done in set_access_flags_filter() - require BOOK3S because we can't support for book3e_hugetlb_preload() called by update_mmu_cache() Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com> --- arch/powerpc/include/asm/book3s/64/pgtable.h | 5 +++++ arch/powerpc/mm/fault.c | 30 +++++++++++++++++++++++++++- 2 files changed, 34 insertions(+), 1 deletion(-)