Re: [PATCH v2 03/11] KVM: arm64: Make kvm_skip_instr() and co private to HYP
From: Marc Zyngier <maz@kernel.org>
Date: 2021-05-05 17:04:01
Also in:
kvm, kvmarm
Subsystem:
arm64 port (aarch64 architecture), kernel virtual machine for arm64 (kvm/arm64), the rest · Maintainers:
Catalin Marinas, Will Deacon, Marc Zyngier, Oliver Upton, Linus Torvalds
Hi Zenghui, 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.
How can you online a CPU using PSCI if that CPU is currently spinning on a WFI? Or is that we have transitioned via userspace to perform the vcpu reset? I can imagine it happening in that case.
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"Ah, the perks of running guests with "quiet"... Well caught.
quoted hunk ↗ jump to hunk
*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... I write the below diff and guess it will help. But I have to look at all other places where we adjust PC directly to make a right fix. Please let me know what do you think. Thanks, Zenghui ---->8----diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c index 956cdc240148..ed647eb387c3 100644 --- a/arch/arm64/kvm/reset.c +++ b/arch/arm64/kvm/reset.c@@ -265,7 +265,12 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) if (vcpu->arch.reset_state.be) kvm_vcpu_set_be(vcpu); + /* + * Don't bother with the KVM_ARM64_INCREMENT_PC flag while + * using this version of __adjust_pc(). + */ *vcpu_pc(vcpu) = target_pc; + vcpu->arch.flags &= ~KVM_ARM64_INCREMENT_PC;
I think you need to make it a lot stronger: any PC-altering flag will do the wrong thing here. I'd go and clear all the exception bits: Thanks, M.
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 956cdc240148..54913612d602 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c@@ -265,6 +265,12 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) if (vcpu->arch.reset_state.be) kvm_vcpu_set_be(vcpu); + /* + * We're reseting the CPU, make sure there is no + * pending exception or other PC-altering event. + */ + vcpu->arch.flags &= ~(KVM_ARM64_PENDING_EXCEPTION | + KVM_ARM64_EXCEPT_MASK); *vcpu_pc(vcpu) = target_pc; vcpu_set_reg(vcpu, 0, vcpu->arch.reset_state.r0);
--
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