linux-kernel - Re: [PATCH] KVM: selftests: Wait mprotect_ro_done before write to RO in mmu_stress

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Message-ID: <23ea46d54e423b30fa71503a823c97213a864a98.camel@intel.com>
Date: Tue, 11 Feb 2025 01:03:08 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: selftests: Wait mprotect_ro_done before write to RO
 in mmu_stress_test

On Sat, 2025-02-08 at 18:53 +0800, Yan Zhao wrote:
> In the read-only mprotect() phase of mmu_stress_test, ensure that
> mprotect(PROT_READ) has completed before the guest starts writing to the
> read-only mprotect() memory.

Is this a fix for the intermittent failure we saw on the v6.13-rc3 based kvm
branch? Funnily, I can't seem to reproduce it anymore, with or without this fix.

On the fix though, doesn't this remove the coverage of writing to a region that
is in the process of being made RO? I'm thinking about warnings, etc that may
trigger intermittently based on bugs with a race component. I don't know if we
could fix the test and still leave the write while the "mprotect(PROT_READ) is
underway". It seems to be deliberate.