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 <[email protected]>
[...]
@@ -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...
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;
vcpu_set_reg(vcpu, 0, vcpu->arch.reset_state.r0);
vcpu->arch.reset_state.reset = false;
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