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Wed, 22 Oct 2025 15:31:58 +0800 From: "Huang, Ying" To: Barry Song <21cnbao@gmail.com> Cc: Catalin Marinas , Will Deacon , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Vlastimil Babka , Zi Yan , Baolin Wang , Ryan Roberts , Yang Shi , "Christoph Lameter (Ampere)" , Dev Jain , Anshuman Khandual , Yicong Yang , Kefeng Wang , Kevin Brodsky , Yin Fengwei , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH -v2 2/2] arm64, tlbflush: don't TLBI broadcast if page reused in write fault In-Reply-To: (Barry Song's message of "Wed, 22 Oct 2025 17:08:47 +1300") References: <20251013092038.6963-1-ying.huang@linux.alibaba.com> <20251013092038.6963-3-ying.huang@linux.alibaba.com> Date: Wed, 22 Oct 2025 15:31:39 +0800 Message-ID: <87a51jfl44.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 646CD40015 X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: gf1aamdbjp9q5h81q5d68skhzx8t8x3o X-HE-Tag: 1761118323-635326 X-HE-Meta: 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 PUgNXXxU g+suSIF23uWB+VzqsmZn0GmR3/aNScSUNud2GSvPfsV0dbiq+0g6ZfmkIka9jV2aBHTjqPBG3PBRqd74nEcYe5LXDnYMm1UFIqfP0RSJvwvNqTwlJymkZ/BIzS4oRyGL2wGvzhLepVeUmnZ9H5lHIoD9QUU6JfsHiROsyXNyC+r/HHlbd1i8Qr1MURYtZZSxCVnF4fmbAHSRyDpU/x2NfFLYeUuENgpvmfYCB8W4D9JXSMXK6dy9+kyEpplqeaC50qPcY5WmCVJ2xD+RlqmQH+axF+9BL8o1F0A0IS/3c/nVjS4Y= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, Barry, Barry Song <21cnbao@gmail.com> writes: >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/p= gtable.h >> index aa89c2e67ebc..35bae2e4bcfe 100644 >> --- a/arch/arm64/include/asm/pgtable.h >> +++ b/arch/arm64/include/asm/pgtable.h >> @@ -130,12 +130,16 @@ static inline void arch_leave_lazy_mmu_mode(void) >> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ >> >> /* >> - * Outside of a few very special situations (e.g. hibernation), we alwa= ys >> - * use broadcast TLB invalidation instructions, therefore a spurious pa= ge >> - * fault on one CPU which has been handled concurrently by another CPU >> - * does not need to perform additional invalidation. >> + * We use local TLB invalidation instruction when reusing page in >> + * write protection fault handler to avoid TLBI broadcast in the hot >> + * path. This will cause spurious page faults if stall read-only TLB >> + * entries exist. >> */ >> -#define flush_tlb_fix_spurious_fault(vma, address, ptep) do { } while (= 0) >> +#define flush_tlb_fix_spurious_fault(vma, address, ptep) \ >> + local_flush_tlb_page_nonotify(vma, address) >> + >> +#define flush_tlb_fix_spurious_fault_pmd(vma, address, pmdp) \ >> + local_flush_tlb_page_nonotify(vma, address) >> >> /* >> * ZERO_PAGE is a global shared page that is always zero: used >> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/= tlbflush.h >> index 18a5dc0c9a54..651b31fd18bb 100644 >> --- a/arch/arm64/include/asm/tlbflush.h >> +++ b/arch/arm64/include/asm/tlbflush.h >> @@ -249,6 +249,18 @@ static inline unsigned long get_trans_granule(void) >> * cannot be easily determined, the value TLBI_TTL_UNKNOWN = will >> * perform a non-hinted invalidation. >> * >> + * local_flush_tlb_page(vma, addr) >> + * Local variant of flush_tlb_page(). Stale TLB entries may >> + * remain in remote CPUs. >> + * >> + * local_flush_tlb_page_nonotify(vma, addr) >> + * Same as local_flush_tlb_page() except MMU notifier will = not be >> + * called. >> + * >> + * local_flush_tlb_contpte_range(vma, start, end) >> + * Invalidate the virtual-address range '[start, end)' mapp= ed with >> + * contpte on local CPU for the user address space correspo= nding >> + * to 'vma->mm'. Stale TLB entries may remain in remote CP= Us. >> * >> * Finally, take a look at asm/tlb.h to see how tlb_flush() is impl= emented >> * on top of these routines, since that is our interface to the mmu= _gather >> @@ -282,6 +294,33 @@ static inline void flush_tlb_mm(struct mm_struct *m= m) >> mmu_notifier_arch_invalidate_secondary_tlbs(mm, 0, -1UL); >> } >> >> +static inline void __local_flush_tlb_page_nonotify_nosync( >> + struct mm_struct *mm, unsigned long uaddr) >> +{ >> + unsigned long addr; >> + >> + dsb(nshst); > > We were issuing dsb(ishst) even for the nosync case, likely to ensure > PTE visibility across cores. However, since set_ptes already includes a > dsb(ishst) in __set_pte_complete(), does this mean we=E2=80=99re being ov= erly > cautious in __flush_tlb_page_nosync() in many cases? > > static inline void __flush_tlb_page_nosync(struct mm_struct *mm, > unsigned long uaddr) > { > unsigned long addr; > > dsb(ishst); > addr =3D __TLBI_VADDR(uaddr, ASID(mm)); > __tlbi(vale1is, addr); > __tlbi_user(vale1is, addr); > mmu_notifier_arch_invalidate_secondary_tlbs(mm, uaddr & PAGE_MASK, > (uaddr & PAGE_MASK) + > PAGE_SIZE); > } IIUC, _nosync() here means doesn't synchronize with the following code. It still synchronizes with the previous code, mainly the page table changing. And, Yes. There may be room to improve this. > On the other hand, __ptep_set_access_flags() doesn=E2=80=99t seem to use > set_ptes(), so there=E2=80=99s no guarantee the updated PTEs are visible = to all > cores. If a remote CPU later encounters a page fault and performs a TLB > invalidation, will it still see a stable PTE? I don't think so. We just flush local TLB in local_flush_tlb_page() family functions. So, we only needs to guarantee the page table changes are available for the local page table walking. If a page fault occurs on a remote CPU, we will call local_flush_tlb_page() on the remote CPU. >> + addr =3D __TLBI_VADDR(uaddr, ASID(mm)); >> + __tlbi(vale1, addr); >> + __tlbi_user(vale1, addr); >> +} >> + >> +static inline void local_flush_tlb_page_nonotify( >> + struct vm_area_struct *vma, unsigned long uaddr) >> +{ >> + __local_flush_tlb_page_nonotify_nosync(vma->vm_mm, uaddr); >> + dsb(nsh); >> +} >> + >> +static inline void local_flush_tlb_page(struct vm_area_struct *vma, >> + unsigned long uaddr) >> +{ >> + __local_flush_tlb_page_nonotify_nosync(vma->vm_mm, uaddr); >> + mmu_notifier_arch_invalidate_secondary_tlbs(vma->vm_mm, uaddr & = PAGE_MASK, >> + (uaddr & PAGE_MASK) + PA= GE_SIZE); >> + dsb(nsh); >> +} >> + >> static inline void __flush_tlb_page_nosync(struct mm_struct *mm, >> unsigned long uaddr) >> { >> @@ -472,6 +511,23 @@ static inline void __flush_tlb_range(struct vm_area= _struct *vma, >> dsb(ish); >> } >> > > We already have functions like > __flush_tlb_page_nosync() and __flush_tlb_range_nosync(). > Is there a way to factor out or extract their common parts? > > Is it because of the differences in barriers that this extraction of > common code isn=E2=80=99t feasible? Yes. It's a good idea to do some code clean to reduce code duplication. Ryan has plan to work on this. --- Best Regards, Huang, Ying