Re: [PATCH v2 03/11] KVM: arm64: Make kvm_skip_instr() and co private to HYP

From: Marc Zyngier <maz@kernel.org>
To: Zenghui Yu <yuzenghui@huawei.com>
Cc: <linux-arm-kernel@lists.infradead.org>,
	<kvmarm@lists.cs.columbia.edu>, <kvm@vger.kernel.org>,
	<kernel-team@android.com>, Will Deacon <will@kernel.org>,
	James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Andrew Scull <ascull@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Quentin Perret <qperret@google.com>,
	David Brazdil <dbrazdil@google.com>
Subject: Re: [PATCH v2 03/11] KVM: arm64: Make kvm_skip_instr() and co private to HYP
Date: Thu, 06 May 2021 18:17:10 +0100	[thread overview]
Message-ID: <87lf8rrdd5.wl-maz@kernel.org> (raw)
In-Reply-To: <cef3517b-e66d-4d26-68a9-2d5fb433377c@huawei.com>

On Wed, 05 May 2021 15:23:02 +0100,
Zenghui Yu <yuzenghui@huawei.com> wrote:
> 
> Hi Marc,
> 
> On 2020/11/3 0:40, Marc Zyngier wrote:
> > In an effort to remove the vcpu PC manipulations from EL1 on nVHE
> > systems, move kvm_skip_instr() to be HYP-specific. EL1's intent
> > to increment PC post emulation is now signalled via a flag in the
> > vcpu structure.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> 
> [...]
> 
> > @@ -133,6 +134,8 @@ static int __kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> >  	__load_guest_stage2(vcpu->arch.hw_mmu);
> >  	__activate_traps(vcpu);
> >  +	__adjust_pc(vcpu);
> 
> If the INCREMENT_PC flag was set (e.g., for WFx emulation) while we're
> handling PSCI CPU_ON call targetting this VCPU, the *target_pc* (aka
> entry point address, normally provided by the primary VCPU) will be
> unexpectedly incremented here. That's pretty bad, I think.
> 
> This was noticed with a latest guest kernel, at least with commit
> dccc9da22ded ("arm64: Improve parking of stopped CPUs"), which put the
> stopped VCPUs in the WFx loop. The guest kernel shouted at me that
> 
> 	"CPU: CPUs started in inconsistent modes"
> 
> *after* rebooting. The problem is that the secondary entry point was
> corrupted by KVM as explained above. All of the secondary processors
> started from set_cpu_boot_mode_flag(), with w0=0. Oh well...

FWIW, I've pushed out a test branch[1] with two patches that sit on
top of Linus' current tree. I'll rebase and post it as soon as -rc1
appears, but I'd appreciate if you could have a look in the meantime.

Thanks,

	M.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/pc-fixes

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