On 5/6/21 3:14 PM, Tom Lendacky wrote:
> When an SEV-ES guest is running, the GHCB is unmapped as part of the
> vCPU run support. However, kvm_vcpu_unmap() triggers an RCU dereference
> warning with CONFIG_PROVE_LOCKING=y because the SRCU lock is released
> before invoking the vCPU run support.
>
> Move the GHCB unmapping into the prepare_guest_switch callback, which is
> invoked while still holding the SRCU lock, eliminating the RCU dereference
> warning.
>
> Fixes: 291bd20d5d88 ("KVM: SVM: Add initial support for a VMGEXIT VMEXIT")
I added the Fixes: tag in case this is to be sent back to stable. But,
5.11 SVM support doesn't have the prepare_guest_switch callback, it was
added in 5.12. This will apply to 5.12 with some fuzz.
Thanks,
Tom
> Reported-by: Borislav Petkov <bp@xxxxxxxxx>
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
> arch/x86/kvm/svm/sev.c | 5 +----
> arch/x86/kvm/svm/svm.c | 3 +++
> arch/x86/kvm/svm/svm.h | 1 +
> 3 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a9d8d6aafdb8..5f70be4e36aa 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2198,7 +2198,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
> return -EINVAL;
> }
>
> -static void pre_sev_es_run(struct vcpu_svm *svm)
> +void sev_es_unmap_ghcb(struct vcpu_svm *svm)
> {
> if (!svm->ghcb)
> return;
> @@ -2234,9 +2234,6 @@ void pre_sev_run(struct vcpu_svm *svm, int cpu)
> struct svm_cpu_data *sd = per_cpu(svm_data, cpu);
> int asid = sev_get_asid(svm->vcpu.kvm);
>
> - /* Perform any SEV-ES pre-run actions */
> - pre_sev_es_run(svm);
> -
> /* Assign the asid allocated with this SEV guest */
> svm->asid = asid;
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index a7271f31df47..e9f9aacc8f51 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1424,6 +1424,9 @@ static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
> struct vcpu_svm *svm = to_svm(vcpu);
> struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
>
> + if (sev_es_guest(vcpu->kvm))
> + sev_es_unmap_ghcb(svm);
> +
> if (svm->guest_state_loaded)
> return;
>
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 84b3133c2251..e44567ceb865 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -581,6 +581,7 @@ void sev_es_init_vmcb(struct vcpu_svm *svm);
> void sev_es_create_vcpu(struct vcpu_svm *svm);
> void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector);
> void sev_es_prepare_guest_switch(struct vcpu_svm *svm, unsigned int cpu);
> +void sev_es_unmap_ghcb(struct vcpu_svm *svm);
>
> /* vmenter.S */
>
>
