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[24.6.216.183]) by smtp.gmail.com with ESMTPSA id 23sm17615107pgk.89.2021.10.05.09.34.07 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 05 Oct 2021 09:34:08 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.120.0.1.13\)) Subject: Re: [PATCH 1/2] mm/mprotect: use mmu_gather From: Nadav Amit In-Reply-To: <20211005065335.GG4323@worktop.programming.kicks-ass.net> Date: Tue, 5 Oct 2021 09:34:06 -0700 Cc: Andrew Morton , LKML , Linux-MM , Peter Xu , Andrea Arcangeli , Andrew Cooper , Andy Lutomirski , Dave Hansen , Thomas Gleixner , Will Deacon , Yu Zhao , Nick Piggin , x86@kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <00EDCFA2-5BFE-4C7A-A41A-DD8902F0E494@gmail.com> References: <20210925205423.168858-1-namit@vmware.com> <20210925205423.168858-2-namit@vmware.com> <20211003121019.GF4323@worktop.programming.kicks-ass.net> <620B1A38-1457-4F77-8666-E73A318392B6@gmail.com> <20211005065335.GG4323@worktop.programming.kicks-ass.net> To: Peter Zijlstra X-Mailer: Apple Mail (2.3654.120.0.1.13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Oct 4, 2021, at 11:53 PM, Peter Zijlstra = wrote: >=20 > On Mon, Oct 04, 2021 at 12:24:14PM -0700, Nadav Amit wrote: >>=20 >>=20 >>> On Oct 3, 2021, at 5:10 AM, Peter Zijlstra = wrote: >>>=20 >>> On Sat, Sep 25, 2021 at 01:54:22PM -0700, Nadav Amit wrote: >>>=20 >>>> @@ -338,25 +344,25 @@ static unsigned long = change_protection_range(struct vm_area_struct *vma, >>>> struct mm_struct *mm =3D vma->vm_mm; >>>> pgd_t *pgd; >>>> unsigned long next; >>>> - unsigned long start =3D addr; >>>> unsigned long pages =3D 0; >>>> + struct mmu_gather tlb; >>>>=20 >>>> BUG_ON(addr >=3D end); >>>> pgd =3D pgd_offset(mm, addr); >>>> flush_cache_range(vma, addr, end); >>>> inc_tlb_flush_pending(mm); >>>=20 >>> That seems unbalanced... >>=20 >> Bad rebase. Thanks for catching it! >>=20 >>>=20 >>>> + tlb_gather_mmu(&tlb, mm); >>>> + tlb_start_vma(&tlb, vma); >>>> do { >>>> next =3D pgd_addr_end(addr, end); >>>> if (pgd_none_or_clear_bad(pgd)) >>>> continue; >>>> - pages +=3D change_p4d_range(vma, pgd, addr, next, = newprot, >>>> + pages +=3D change_p4d_range(&tlb, vma, pgd, addr, next, = newprot, >>>> cp_flags); >>>> } while (pgd++, addr =3D next, addr !=3D end); >>>>=20 >>>> - /* Only flush the TLB if we actually modified any entries: */ >>>> - if (pages) >>>> - flush_tlb_range(vma, start, end); >>>> - dec_tlb_flush_pending(mm); >>>=20 >>> ... seeing you do remove the extra decrement. >>=20 >> Is it really needed? We do not put this comment elsewhere for >> tlb_finish_mmu(). But no problem, I=E2=80=99ll keep it. >=20 > -ENOPARSE, did you read decrement as comment? In any case, I don't > particularly care about the comment, and tlb_*_mmu() imply the inc/dec > thingies. >=20 > All I tried to do is point out that removing the dec but leaving the = inc > is somewhat inconsistent :-) The autocorrect in my mind was broken so I read as =E2=80=9Cdocumentation=E2= =80=9D instead of =E2=80=9Cdecrement=E2=80=9D. I will send v2 soon. Thanks again! Nadav=20=