On Wed, 05 May 2021 15:23:02 +0100,
Zenghui Yu [off-list ref] wrote:

Hi Marc,

On 2020/11/3 0:40, Marc Zyngier wrote:

quoted

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>

[...]

quoted

@@ -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.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel