linux-kernel - Re: [PATCH v12 54/84] KVM: arm64: Mark "struct page" pfns accessed/dirty before dropping mmu

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Message-ID: <86ikwe2fph.wl-maz@kernel.org>
Date: Tue, 06 Aug 2024 09:55:22 +0100
From: Marc Zyngier <maz@...nel.org>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	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>,
	Fuad Tabba <tabba@...gle.com>
Subject: Re: [PATCH v12 54/84] KVM: arm64: Mark "struct page" pfns accessed/dirty before dropping mmu_lock

On Tue, 06 Aug 2024 00:26:54 +0100,
Oliver Upton <oliver.upton@...ux.dev> wrote:
> 
> 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.

Should we consider reverting 9c30fc615daa then?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.