[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZrFfgzRbiqT-Zi2O@linux.dev>
Date: Mon, 5 Aug 2024 23:25:55 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
Tianrui Zhao <zhaotianrui@...ngson.cn>,
Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
Anup Patel <anup@...infault.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
David Matlack <dmatlack@...gle.com>,
David Stevens <stevensd@...omium.org>
Subject: Re: [PATCH v12 54/84] KVM: arm64: Mark "struct page" pfns
accessed/dirty before dropping mmu_lock
[+cc Fuad]
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 <seanjc@...gle.com>
> ---
> 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
Powered by blists - more mailing lists