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From: Oliver Upton To: Sean Christopherson Subject: Re: [PATCH v12 54/84] KVM: arm64: Mark "struct page" pfns accessed/dirty before dropping mmu_lock Message-ID: References: <20240726235234.228822-1-seanjc@google.com> <20240726235234.228822-55-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, David Matlack , linux-riscv@lists.infradead.org, Claudio Imbrenda , Marc Zyngier , Janosch Frank , Huacai Chen , Fuad Tabba , Christian Borntraeger , Albert Ou , Bibo Mao , loongarch@lists.linux.dev, Paul Walmsley , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, Palmer Dabbelt , David Stevens , kvm-riscv@lists.infradead.org, Anup Patel , Paolo Bonzini , Tianrui Zhao , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Aug 05, 2024 at 11:26:03PM +0000, Oliver Upton wrote: > [+cc Fuad] Take 2! > Fuad, you mentioned in commit 9c30fc615daa ("KVM: arm64: Move setting > the page as dirty out of the critical section") that restructuring > around the MMU lock was helpful for reuse (presumably for pKVM), but I > lack the context there. > > On Fri, Jul 26, 2024 at 04:52:03PM -0700, Sean Christopherson wrote: > > Mark pages/folios accessed+dirty prior to dropping mmu_lock, as marking a > > page/folio dirty after it has been written back can make some filesystems > > unhappy (backing KVM guests will such filesystem files is uncommon, and > > typo: s/will/with/ > > > the race is minuscule, hence the lack of complaints). See the link below > > for details. > > > > This will also allow converting arm64 to kvm_release_faultin_page(), which > > requires that mmu_lock be held (for the aforementioned reason). > > > > Link: https://lore.kernel.org/all/cover.1683044162.git.lstoakes@gmail.com > > Signed-off-by: Sean Christopherson > > --- > > arch/arm64/kvm/mmu.c | 10 ++++++---- > > 1 file changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > > index 22ee37360c4e..ce13c3d884d5 100644 > > --- a/arch/arm64/kvm/mmu.c > > +++ b/arch/arm64/kvm/mmu.c > > @@ -1685,15 +1685,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > > } > > > > out_unlock: > > + if (writable && !ret) > > + kvm_set_pfn_dirty(pfn); > > I'm guessing you meant kvm_release_pfn_dirty() here, because this leaks > a reference. > > > + else > > + kvm_release_pfn_clean(pfn); > > + > > read_unlock(&kvm->mmu_lock); > > > > /* Mark the page dirty only if the fault is handled successfully */ > > - if (writable && !ret) { > > - kvm_set_pfn_dirty(pfn); > > + if (writable && !ret) > > mark_page_dirty_in_slot(kvm, memslot, gfn); > > - } > > > > - kvm_release_pfn_clean(pfn); > > return ret != -EAGAIN ? ret : 0; > > } > > > > -- > > 2.46.0.rc1.232.g9752f9e123-goog > > > > -- > Thanks, > Oliver -- Thanks, Oliver