kvm.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
* [PATCH] KVM: SVM: Move GHCB unmapping to fix RCU warning
@ 2021-05-06 20:14 Tom Lendacky
  2021-05-06 20:31 ` Tom Lendacky
  0 siblings, 1 reply; 2+ messages in thread
From: Tom Lendacky @ 2021-05-06 20:14 UTC (permalink / raw)
  To: kvm, linux-kernel, x86
  Cc: Paolo Bonzini, Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li,
	Jim Mattson, Joerg Roedel, Thomas Gleixner, Ingo Molnar,
	Borislav Petkov, Brijesh Singh

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")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 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 */
 
-- 
2.31.0


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH] KVM: SVM: Move GHCB unmapping to fix RCU warning
  2021-05-06 20:14 [PATCH] KVM: SVM: Move GHCB unmapping to fix RCU warning Tom Lendacky
@ 2021-05-06 20:31 ` Tom Lendacky
  0 siblings, 0 replies; 2+ messages in thread
From: Tom Lendacky @ 2021-05-06 20:31 UTC (permalink / raw)
  To: kvm, linux-kernel, x86
  Cc: Paolo Bonzini, Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li,
	Jim Mattson, Joerg Roedel, Thomas Gleixner, Ingo Molnar,
	Borislav Petkov, Brijesh Singh

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@alien8.de>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  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 */
>  
> 

^ permalink raw reply	[flat|nested] 2+ messages in thread

end of thread, other threads:[~2021-05-06 20:31 UTC | newest]

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-05-06 20:14 [PATCH] KVM: SVM: Move GHCB unmapping to fix RCU warning Tom Lendacky
2021-05-06 20:31 ` Tom Lendacky

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).