| Message ID | 20231207150348.82096-4-alexghiti@rivosinc.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Remove preventive sfence.vma | expand |
The subject says "riscv:" but it changes core part and several arch. Maybe this commit should be split in two commits, one for API changes that changes flush_tlb_fix_spurious_fault() to flush_tlb_fix_spurious_write_fault() and adds flush_tlb_fix_spurious_read_fault() including the change in memory.c, then a second patch with the changes to riscv. Le 07/12/2023 à 16:03, Alexandre Ghiti a écrit : > The preventive sfence.vma were emitted because new mappings must be made > visible to the page table walker, either the uarch caches invalid > entries or not. > > Actually, there is no need to preventively sfence.vma on new mappings for > userspace, this should be handled only in the page fault path. > > This allows to drastically reduce the number of sfence.vma emitted: > > * Ubuntu boot to login: > Before: ~630k sfence.vma > After: ~200k sfence.vma > > * ltp - mmapstress01 > Before: ~45k > After: ~6.3k > > * lmbench - lat_pagefault > Before: ~665k > After: 832 (!) > > * lmbench - lat_mmap > Before: ~546k > After: 718 (!) > > The only issue with the removal of sfence.vma in update_mmu_cache() is > that on uarchs that cache invalid entries, those won't be invalidated > until the process takes a fault: so that's an additional fault in those > cases. > > Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> > --- > arch/arm64/include/asm/pgtable.h | 2 +- > arch/mips/include/asm/pgtable.h | 6 +-- > arch/powerpc/include/asm/book3s/64/tlbflush.h | 8 ++-- > arch/riscv/include/asm/pgtable.h | 43 +++++++++++-------- > include/linux/pgtable.h | 8 +++- > mm/memory.c | 12 +++++- > 6 files changed, 48 insertions(+), 31 deletions(-) Did you forget mm/pgtable-generic.c ? > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 7f7d9b1df4e5..728f25f529a5 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -57,7 +57,7 @@ static inline bool arch_thp_swp_supported(void) > * fault on one CPU which has been handled concurrently by another CPU > * does not need to perform additional invalidation. > */ > -#define flush_tlb_fix_spurious_fault(vma, address, ptep) do { } while (0) > +#define flush_tlb_fix_spurious_write_fault(vma, address, ptep) do { } while (0) Why do you need to do that change ? Nothing is explained about that in the commit message. > > /* > * ZERO_PAGE is a global shared page that is always zero: used > diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h > index 430b208c0130..84439fe6ed29 100644 > --- a/arch/mips/include/asm/pgtable.h > +++ b/arch/mips/include/asm/pgtable.h > @@ -478,9 +478,9 @@ static inline pgprot_t pgprot_writecombine(pgprot_t _prot) > return __pgprot(prot); > } > > -static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, > - unsigned long address, > - pte_t *ptep) > +static inline void flush_tlb_fix_spurious_write_fault(struct vm_area_struct *vma, > + unsigned long address, > + pte_t *ptep) > { > } > > diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h > index 1950c1b825b4..7166d56f90db 100644 > --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h > +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h > @@ -128,10 +128,10 @@ static inline void flush_tlb_page(struct vm_area_struct *vma, > #define flush_tlb_page(vma, addr) local_flush_tlb_page(vma, addr) > #endif /* CONFIG_SMP */ > > -#define flush_tlb_fix_spurious_fault flush_tlb_fix_spurious_fault > -static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, > - unsigned long address, > - pte_t *ptep) > +#define flush_tlb_fix_spurious_write_fault flush_tlb_fix_spurious_write_fault > +static inline void flush_tlb_fix_spurious_write_fault(struct vm_area_struct *vma, > + unsigned long address, > + pte_t *ptep) > { > /* > * Book3S 64 does not require spurious fault flushes because the PTE > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h > index b2ba3f79cfe9..89aa5650f104 100644 > --- a/arch/riscv/include/asm/pgtable.h > +++ b/arch/riscv/include/asm/pgtable.h > @@ -472,28 +472,20 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf, > struct vm_area_struct *vma, unsigned long address, > pte_t *ptep, unsigned int nr) > { > - /* > - * The kernel assumes that TLBs don't cache invalid entries, but > - * in RISC-V, SFENCE.VMA specifies an ordering constraint, not a > - * cache flush; it is necessary even after writing invalid entries. > - * Relying on flush_tlb_fix_spurious_fault would suffice, but > - * the extra traps reduce performance. So, eagerly SFENCE.VMA. > - */ > - while (nr--) > - local_flush_tlb_page(address + nr * PAGE_SIZE); > } > #define update_mmu_cache(vma, addr, ptep) \ > update_mmu_cache_range(NULL, vma, addr, ptep, 1) > > #define __HAVE_ARCH_UPDATE_MMU_TLB > -#define update_mmu_tlb update_mmu_cache > +static inline void update_mmu_tlb(struct vm_area_struct *vma, > + unsigned long address, pte_t *ptep) > +{ > + flush_tlb_range(vma, address, address + PAGE_SIZE); > +} > > static inline void update_mmu_cache_pmd(struct vm_area_struct *vma, > unsigned long address, pmd_t *pmdp) > { > - pte_t *ptep = (pte_t *)pmdp; > - > - update_mmu_cache(vma, address, ptep); > } > > #define __HAVE_ARCH_PTE_SAME > @@ -548,13 +540,26 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, > unsigned long address, pte_t *ptep, > pte_t entry, int dirty) > { > - if (!pte_same(*ptep, entry)) > + if (!pte_same(*ptep, entry)) { > __set_pte_at(ptep, entry); > - /* > - * update_mmu_cache will unconditionally execute, handling both > - * the case that the PTE changed and the spurious fault case. > - */ > - return true; > + /* Here only not svadu is impacted */ > + flush_tlb_page(vma, address); > + return true; > + } > + > + return false; > +} > + > +extern u64 nr_sfence_vma_handle_exception; > +extern bool tlb_caching_invalid_entries; > + > +#define flush_tlb_fix_spurious_read_fault flush_tlb_fix_spurious_read_fault > +static inline void flush_tlb_fix_spurious_read_fault(struct vm_area_struct *vma, > + unsigned long address, > + pte_t *ptep) > +{ > + if (tlb_caching_invalid_entries) > + flush_tlb_page(vma, address); > } > > #define __HAVE_ARCH_PTEP_GET_AND_CLEAR > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index af7639c3b0a3..7abaf42ef612 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -931,8 +931,12 @@ static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio) > # define pte_accessible(mm, pte) ((void)(pte), 1) > #endif > > -#ifndef flush_tlb_fix_spurious_fault > -#define flush_tlb_fix_spurious_fault(vma, address, ptep) flush_tlb_page(vma, address) > +#ifndef flush_tlb_fix_spurious_write_fault > +#define flush_tlb_fix_spurious_write_fault(vma, address, ptep) flush_tlb_page(vma, address) > +#endif > + > +#ifndef flush_tlb_fix_spurious_read_fault > +#define flush_tlb_fix_spurious_read_fault(vma, address, ptep) > #endif > > /* > diff --git a/mm/memory.c b/mm/memory.c > index 517221f01303..5cb0ccf0c03f 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5014,8 +5014,16 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) > * with threads. > */ > if (vmf->flags & FAULT_FLAG_WRITE) > - flush_tlb_fix_spurious_fault(vmf->vma, vmf->address, > - vmf->pte); > + flush_tlb_fix_spurious_write_fault(vmf->vma, vmf->address, > + vmf->pte); > + else > + /* > + * With the pte_same(ptep_get(vmf->pte), entry) check > + * that calls update_mmu_tlb() above, multiple threads > + * faulting at the same time won't get there. > + */ > + flush_tlb_fix_spurious_read_fault(vmf->vma, vmf->address, > + vmf->pte); > } > unlock: > pte_unmap_unlock(vmf->pte, vmf->ptl);
On Thu, Dec 7, 2023 at 5:37 PM Christophe Leroy <christophe.leroy@csgroup.eu> wrote: > > The subject says "riscv:" but it changes core part and several arch. > Maybe this commit should be split in two commits, one for API changes > that changes flush_tlb_fix_spurious_fault() to > flush_tlb_fix_spurious_write_fault() and adds > flush_tlb_fix_spurious_read_fault() including the change in memory.c, > then a second patch with the changes to riscv. You're right, I'll do that, thanks. > > Le 07/12/2023 à 16:03, Alexandre Ghiti a écrit : > > The preventive sfence.vma were emitted because new mappings must be made > > visible to the page table walker, either the uarch caches invalid > > entries or not. > > > > Actually, there is no need to preventively sfence.vma on new mappings for > > userspace, this should be handled only in the page fault path. > > > > This allows to drastically reduce the number of sfence.vma emitted: > > > > * Ubuntu boot to login: > > Before: ~630k sfence.vma > > After: ~200k sfence.vma > > > > * ltp - mmapstress01 > > Before: ~45k > > After: ~6.3k > > > > * lmbench - lat_pagefault > > Before: ~665k > > After: 832 (!) > > > > * lmbench - lat_mmap > > Before: ~546k > > After: 718 (!) > > > > The only issue with the removal of sfence.vma in update_mmu_cache() is > > that on uarchs that cache invalid entries, those won't be invalidated > > until the process takes a fault: so that's an additional fault in those > > cases. > > > > Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> > > --- > > arch/arm64/include/asm/pgtable.h | 2 +- > > arch/mips/include/asm/pgtable.h | 6 +-- > > arch/powerpc/include/asm/book3s/64/tlbflush.h | 8 ++-- > > arch/riscv/include/asm/pgtable.h | 43 +++++++++++-------- > > include/linux/pgtable.h | 8 +++- > > mm/memory.c | 12 +++++- > > 6 files changed, 48 insertions(+), 31 deletions(-) > > Did you forget mm/pgtable-generic.c ? Indeed, I "missed" the occurrence of flush_tlb_fix_spurious_fault() there, thanks. > > > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > index 7f7d9b1df4e5..728f25f529a5 100644 > > --- a/arch/arm64/include/asm/pgtable.h > > +++ b/arch/arm64/include/asm/pgtable.h > > @@ -57,7 +57,7 @@ static inline bool arch_thp_swp_supported(void) > > * fault on one CPU which has been handled concurrently by another CPU > > * does not need to perform additional invalidation. > > */ > > -#define flush_tlb_fix_spurious_fault(vma, address, ptep) do { } while (0) > > +#define flush_tlb_fix_spurious_write_fault(vma, address, ptep) do { } while (0) > > Why do you need to do that change ? Nothing is explained about that in > the commit message. I renamed this macro because in the page fault path, flush_tlb_fix_spurious_fault() is called only when the fault is a write fault (see https://elixir.bootlin.com/linux/latest/source/mm/memory.c#L5016). I'll check if that fits the occurrence in mm/pgtable-generic.c too. Thanks again for the review, Alex > > > > > /* > > * ZERO_PAGE is a global shared page that is always zero: used > > diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h > > index 430b208c0130..84439fe6ed29 100644 > > --- a/arch/mips/include/asm/pgtable.h > > +++ b/arch/mips/include/asm/pgtable.h > > @@ -478,9 +478,9 @@ static inline pgprot_t pgprot_writecombine(pgprot_t _prot) > > return __pgprot(prot); > > } > > > > -static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, > > - unsigned long address, > > - pte_t *ptep) > > +static inline void flush_tlb_fix_spurious_write_fault(struct vm_area_struct *vma, > > + unsigned long address, > > + pte_t *ptep) > > { > > } > > > > diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h > > index 1950c1b825b4..7166d56f90db 100644 > > --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h > > +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h > > @@ -128,10 +128,10 @@ static inline void flush_tlb_page(struct vm_area_struct *vma, > > #define flush_tlb_page(vma, addr) local_flush_tlb_page(vma, addr) > > #endif /* CONFIG_SMP */ > > > > -#define flush_tlb_fix_spurious_fault flush_tlb_fix_spurious_fault > > -static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, > > - unsigned long address, > > - pte_t *ptep) > > +#define flush_tlb_fix_spurious_write_fault flush_tlb_fix_spurious_write_fault > > +static inline void flush_tlb_fix_spurious_write_fault(struct vm_area_struct *vma, > > + unsigned long address, > > + pte_t *ptep) > > { > > /* > > * Book3S 64 does not require spurious fault flushes because the PTE > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h > > index b2ba3f79cfe9..89aa5650f104 100644 > > --- a/arch/riscv/include/asm/pgtable.h > > +++ b/arch/riscv/include/asm/pgtable.h > > @@ -472,28 +472,20 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf, > > struct vm_area_struct *vma, unsigned long address, > > pte_t *ptep, unsigned int nr) > > { > > - /* > > - * The kernel assumes that TLBs don't cache invalid entries, but > > - * in RISC-V, SFENCE.VMA specifies an ordering constraint, not a > > - * cache flush; it is necessary even after writing invalid entries. > > - * Relying on flush_tlb_fix_spurious_fault would suffice, but > > - * the extra traps reduce performance. So, eagerly SFENCE.VMA. > > - */ > > - while (nr--) > > - local_flush_tlb_page(address + nr * PAGE_SIZE); > > } > > #define update_mmu_cache(vma, addr, ptep) \ > > update_mmu_cache_range(NULL, vma, addr, ptep, 1) > > > > #define __HAVE_ARCH_UPDATE_MMU_TLB > > -#define update_mmu_tlb update_mmu_cache > > +static inline void update_mmu_tlb(struct vm_area_struct *vma, > > + unsigned long address, pte_t *ptep) > > +{ > > + flush_tlb_range(vma, address, address + PAGE_SIZE); > > +} > > > > static inline void update_mmu_cache_pmd(struct vm_area_struct *vma, > > unsigned long address, pmd_t *pmdp) > > { > > - pte_t *ptep = (pte_t *)pmdp; > > - > > - update_mmu_cache(vma, address, ptep); > > } > > > > #define __HAVE_ARCH_PTE_SAME > > @@ -548,13 +540,26 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, > > unsigned long address, pte_t *ptep, > > pte_t entry, int dirty) > > { > > - if (!pte_same(*ptep, entry)) > > + if (!pte_same(*ptep, entry)) { > > __set_pte_at(ptep, entry); > > - /* > > - * update_mmu_cache will unconditionally execute, handling both > > - * the case that the PTE changed and the spurious fault case. > > - */ > > - return true; > > + /* Here only not svadu is impacted */ > > + flush_tlb_page(vma, address); > > + return true; > > + } > > + > > + return false; > > +} > > + > > +extern u64 nr_sfence_vma_handle_exception; > > +extern bool tlb_caching_invalid_entries; > > + > > +#define flush_tlb_fix_spurious_read_fault flush_tlb_fix_spurious_read_fault > > +static inline void flush_tlb_fix_spurious_read_fault(struct vm_area_struct *vma, > > + unsigned long address, > > + pte_t *ptep) > > +{ > > + if (tlb_caching_invalid_entries) > > + flush_tlb_page(vma, address); > > } > > > > #define __HAVE_ARCH_PTEP_GET_AND_CLEAR > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > > index af7639c3b0a3..7abaf42ef612 100644 > > --- a/include/linux/pgtable.h > > +++ b/include/linux/pgtable.h > > @@ -931,8 +931,12 @@ static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio) > > # define pte_accessible(mm, pte) ((void)(pte), 1) > > #endif > > > > -#ifndef flush_tlb_fix_spurious_fault > > -#define flush_tlb_fix_spurious_fault(vma, address, ptep) flush_tlb_page(vma, address) > > +#ifndef flush_tlb_fix_spurious_write_fault > > +#define flush_tlb_fix_spurious_write_fault(vma, address, ptep) flush_tlb_page(vma, address) > > +#endif > > + > > +#ifndef flush_tlb_fix_spurious_read_fault > > +#define flush_tlb_fix_spurious_read_fault(vma, address, ptep) > > #endif > > > > /* > > diff --git a/mm/memory.c b/mm/memory.c > > index 517221f01303..5cb0ccf0c03f 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -5014,8 +5014,16 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) > > * with threads. > > */ > > if (vmf->flags & FAULT_FLAG_WRITE) > > - flush_tlb_fix_spurious_fault(vmf->vma, vmf->address, > > - vmf->pte); > > + flush_tlb_fix_spurious_write_fault(vmf->vma, vmf->address, > > + vmf->pte); > > + else > > + /* > > + * With the pte_same(ptep_get(vmf->pte), entry) check > > + * that calls update_mmu_tlb() above, multiple threads > > + * faulting at the same time won't get there. > > + */ > > + flush_tlb_fix_spurious_read_fault(vmf->vma, vmf->address, > > + vmf->pte); > > } > > unlock: > > pte_unmap_unlock(vmf->pte, vmf->ptl);
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 7f7d9b1df4e5..728f25f529a5 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -57,7 +57,7 @@ static inline bool arch_thp_swp_supported(void) * fault on one CPU which has been handled concurrently by another CPU * does not need to perform additional invalidation. */ -#define flush_tlb_fix_spurious_fault(vma, address, ptep) do { } while (0) +#define flush_tlb_fix_spurious_write_fault(vma, address, ptep) do { } while (0) /* * ZERO_PAGE is a global shared page that is always zero: used diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h index 430b208c0130..84439fe6ed29 100644 --- a/arch/mips/include/asm/pgtable.h +++ b/arch/mips/include/asm/pgtable.h @@ -478,9 +478,9 @@ static inline pgprot_t pgprot_writecombine(pgprot_t _prot) return __pgprot(prot); } -static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, - unsigned long address, - pte_t *ptep) +static inline void flush_tlb_fix_spurious_write_fault(struct vm_area_struct *vma, + unsigned long address, + pte_t *ptep) { } diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h index 1950c1b825b4..7166d56f90db 100644 --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h @@ -128,10 +128,10 @@ static inline void flush_tlb_page(struct vm_area_struct *vma, #define flush_tlb_page(vma, addr) local_flush_tlb_page(vma, addr) #endif /* CONFIG_SMP */ -#define flush_tlb_fix_spurious_fault flush_tlb_fix_spurious_fault -static inline void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma, - unsigned long address, - pte_t *ptep) +#define flush_tlb_fix_spurious_write_fault flush_tlb_fix_spurious_write_fault +static inline void flush_tlb_fix_spurious_write_fault(struct vm_area_struct *vma, + unsigned long address, + pte_t *ptep) { /* * Book3S 64 does not require spurious fault flushes because the PTE diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h index b2ba3f79cfe9..89aa5650f104 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -472,28 +472,20 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf, struct vm_area_struct *vma, unsigned long address, pte_t *ptep, unsigned int nr) { - /* - * The kernel assumes that TLBs don't cache invalid entries, but - * in RISC-V, SFENCE.VMA specifies an ordering constraint, not a - * cache flush; it is necessary even after writing invalid entries. - * Relying on flush_tlb_fix_spurious_fault would suffice, but - * the extra traps reduce performance. So, eagerly SFENCE.VMA. - */ - while (nr--) - local_flush_tlb_page(address + nr * PAGE_SIZE); } #define update_mmu_cache(vma, addr, ptep) \ update_mmu_cache_range(NULL, vma, addr, ptep, 1) #define __HAVE_ARCH_UPDATE_MMU_TLB -#define update_mmu_tlb update_mmu_cache +static inline void update_mmu_tlb(struct vm_area_struct *vma, + unsigned long address, pte_t *ptep) +{ + flush_tlb_range(vma, address, address + PAGE_SIZE); +} static inline void update_mmu_cache_pmd(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp) { - pte_t *ptep = (pte_t *)pmdp; - - update_mmu_cache(vma, address, ptep); } #define __HAVE_ARCH_PTE_SAME @@ -548,13 +540,26 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address, pte_t *ptep, pte_t entry, int dirty) { - if (!pte_same(*ptep, entry)) + if (!pte_same(*ptep, entry)) { __set_pte_at(ptep, entry); - /* - * update_mmu_cache will unconditionally execute, handling both - * the case that the PTE changed and the spurious fault case. - */ - return true; + /* Here only not svadu is impacted */ + flush_tlb_page(vma, address); + return true; + } + + return false; +} + +extern u64 nr_sfence_vma_handle_exception; +extern bool tlb_caching_invalid_entries; + +#define flush_tlb_fix_spurious_read_fault flush_tlb_fix_spurious_read_fault +static inline void flush_tlb_fix_spurious_read_fault(struct vm_area_struct *vma, + unsigned long address, + pte_t *ptep) +{ + if (tlb_caching_invalid_entries) + flush_tlb_page(vma, address); } #define __HAVE_ARCH_PTEP_GET_AND_CLEAR diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index af7639c3b0a3..7abaf42ef612 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -931,8 +931,12 @@ static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio) # define pte_accessible(mm, pte) ((void)(pte), 1) #endif -#ifndef flush_tlb_fix_spurious_fault -#define flush_tlb_fix_spurious_fault(vma, address, ptep) flush_tlb_page(vma, address) +#ifndef flush_tlb_fix_spurious_write_fault +#define flush_tlb_fix_spurious_write_fault(vma, address, ptep) flush_tlb_page(vma, address) +#endif + +#ifndef flush_tlb_fix_spurious_read_fault +#define flush_tlb_fix_spurious_read_fault(vma, address, ptep) #endif /* diff --git a/mm/memory.c b/mm/memory.c index 517221f01303..5cb0ccf0c03f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5014,8 +5014,16 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) * with threads. */ if (vmf->flags & FAULT_FLAG_WRITE) - flush_tlb_fix_spurious_fault(vmf->vma, vmf->address, - vmf->pte); + flush_tlb_fix_spurious_write_fault(vmf->vma, vmf->address, + vmf->pte); + else + /* + * With the pte_same(ptep_get(vmf->pte), entry) check + * that calls update_mmu_tlb() above, multiple threads + * faulting at the same time won't get there. + */ + flush_tlb_fix_spurious_read_fault(vmf->vma, vmf->address, + vmf->pte); } unlock: pte_unmap_unlock(vmf->pte, vmf->ptl);
The preventive sfence.vma were emitted because new mappings must be made visible to the page table walker, either the uarch caches invalid entries or not. Actually, there is no need to preventively sfence.vma on new mappings for userspace, this should be handled only in the page fault path. This allows to drastically reduce the number of sfence.vma emitted: * Ubuntu boot to login: Before: ~630k sfence.vma After: ~200k sfence.vma * ltp - mmapstress01 Before: ~45k After: ~6.3k * lmbench - lat_pagefault Before: ~665k After: 832 (!) * lmbench - lat_mmap Before: ~546k After: 718 (!) The only issue with the removal of sfence.vma in update_mmu_cache() is that on uarchs that cache invalid entries, those won't be invalidated until the process takes a fault: so that's an additional fault in those cases. Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> --- arch/arm64/include/asm/pgtable.h | 2 +- arch/mips/include/asm/pgtable.h | 6 +-- arch/powerpc/include/asm/book3s/64/tlbflush.h | 8 ++-- arch/riscv/include/asm/pgtable.h | 43 +++++++++++-------- include/linux/pgtable.h | 8 +++- mm/memory.c | 12 +++++- 6 files changed, 48 insertions(+), 31 deletions(-)