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AJvYcCUYlNRjIWPo0FR0t4BoIKxGZWCxR6qBX4exeHuJZa6Bp+OLXaqEMg5Lg5qIR13zQxcsZ85kVqRWTIxx6yXtBaxuV6U= X-Gm-Message-State: AOJu0Yx//CSf1COmePFEk/uGxUY8RYMb6ScsgtxSwKe9tnRTIK65yJbq tJIySxsdX+h8bWg8F6leNih3ip3tDNAIl5nG6Jle+ExBxe6wOdvqwiUjIa5ARHWHmjxmW9gVE4N KkWeMOwZ3cLyeSuXXziSn3OO0wVWczQYmYDxp2Q== X-Google-Smtp-Source: AGHT+IGQo/4+Bcec7GR4w4t9VuGgDnfgRuIzi4gbmVB9EXNZxFk4++tYC42KZVEUtna/+lcQBmHO84N93cneyoHhbbs= X-Received: by 2002:a05:6871:3329:b0:24c:ac96:ac78 with SMTP id 586e51a60fabf-25060de9e8amr1722957fac.44.1717061727430; Thu, 30 May 2024 02:35:27 -0700 (PDT) MIME-Version: 1.0 References: <20240131155929.169961-1-alexghiti@rivosinc.com> <20240131155929.169961-5-alexghiti@rivosinc.com> In-Reply-To: <20240131155929.169961-5-alexghiti@rivosinc.com> From: yunhui cui Date: Thu, 30 May 2024 17:35:16 +0800 Message-ID: Subject: Re: [External] [PATCH RFC/RFT v2 4/4] riscv: Stop emitting preventive sfence.vma for new userspace mappings with Svvptc To: Alexandre Ghiti Cc: Catalin Marinas , Will Deacon , Thomas Bogendoerfer , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Paul Walmsley , Palmer Dabbelt , Albert Ou , Andrew Morton , Ved Shanbhogue , Matt Evans , Dylan Jhong , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: BC04C40008 X-Stat-Signature: s49gzq5bu4ptar4hcrjkymp3orq1utag X-HE-Tag: 1717061728-435846 X-HE-Meta: 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 fFIRsHxb g7sVYCUEJmIyiIBNv/0hRy8nkXHrWxlOl6rh7l8qXSZcVUMS7qSk/0JALqausSwEzUsN+kiqVrpT1RN8iu74FErUhAixg2jnhjVyL0yYQrWc11pHSYyxy3bxAFMvgrVc2r6lETQH2H6Z+He1zm4UprPtDK8f2a0ZNKc2QiLIyPCx777flIZquzLUGZF2NrOpzDa9XuZ21oM6fq/1WJeB2ZQb1vCR1y5DWc08DALNrlB6h2BBxUo/TqOCI4P8F5YD5UjVPVH0IggCcTVzSBmui4iCn1lFTWtEcaZFwhMI4CL7sAmo= 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 Alex, On Thu, Feb 1, 2024 at 12:04=E2=80=AFAM Alexandre Ghiti wrote: > > The preventive sfence.vma were emitted because new mappings must be made > visible to the page table walker but Svvptc guarantees that xRET act as > a fence, so no need to sfence.vma for the uarchs that implement this > extension. > > 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 (!) > > Signed-off-by: Alexandre Ghiti > --- > arch/riscv/include/asm/pgtable.h | 16 +++++++++++++++- > arch/riscv/mm/pgtable.c | 13 +++++++++++++ > 2 files changed, 28 insertions(+), 1 deletion(-) > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pg= table.h > index 0c94260b5d0c..50986e4c4601 100644 > --- a/arch/riscv/include/asm/pgtable.h > +++ b/arch/riscv/include/asm/pgtable.h > @@ -473,6 +473,9 @@ static inline void update_mmu_cache_range(struct vm_f= ault *vmf, > struct vm_area_struct *vma, unsigned long address, > pte_t *ptep, unsigned int nr) > { > + asm_volatile_goto(ALTERNATIVE("nop", "j %l[svvptc]", 0, RISCV_ISA= _EXT_SVVPTC, 1) > + : : : : svvptc); > + > /* > * The kernel assumes that TLBs don't cache invalid entries, but > * in RISC-V, SFENCE.VMA specifies an ordering constraint, not a > @@ -482,12 +485,23 @@ static inline void update_mmu_cache_range(struct vm= _fault *vmf, > */ > while (nr--) > local_flush_tlb_page(address + nr * PAGE_SIZE); > + > +svvptc: > + /* > + * Svvptc guarantees that xRET act as a fence, so when the uarch = does > + * not cache invalid entries, we don't have to do anything. > + */ > + ; > } >From the perspective of RISC-V arch, the logic of this patch is reasonable. The code of mm comm submodule may be missing update_mmu_cache_range(), for example: there is no flush TLB in remap_pte_range() after updating pte. I will send a patch to mm/ to fix this problem next. Thanks, Yunhui