2023-09-28 20:37:42

by Maxim Levitsky

Subject: [PATCH 2/5] x86: KVM: SVM: add support for Invalid IPI Vector interception

In later revisions of AMD's APM, there is a new 'incomplete IPI' exit code:

"Invalid IPI Vector - The vector for the specified IPI was set to an
illegal value (VEC < 16)"

Note that tests on Zen2 machine show that this VM exit doesn't happen and
instead AVIC just does nothing.

Add support for this exit code by doing nothing, instead of filling
the kernel log with errors.

Also replace an unthrottled 'pr_err()' if another unknown incomplete
IPI exit happens with WARN_ON_ONCE()

(e.g in case AMD adds yet another 'Invalid IPI' exit reason)

Cc: <[email protected]>

Signed-off-by: Maxim Levitsky <[email protected]>
---
arch/x86/include/asm/svm.h | 1 +
arch/x86/kvm/svm/avic.c | 5 ++++-
2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 19bf955b67e0da0..3ac0ffc4f3e202b 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -268,6 +268,7 @@ enum avic_ipi_failure_cause {
AVIC_IPI_FAILURE_TARGET_NOT_RUNNING,
AVIC_IPI_FAILURE_INVALID_TARGET,
AVIC_IPI_FAILURE_INVALID_BACKING_PAGE,
+ AVIC_IPI_FAILURE_INVALID_IPI_VECTOR,
};

#define AVIC_PHYSICAL_MAX_INDEX_MASK GENMASK_ULL(8, 0)
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 2092db892d7d052..c44b65af494e3ff 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -529,8 +529,11 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
case AVIC_IPI_FAILURE_INVALID_BACKING_PAGE:
WARN_ONCE(1, "Invalid backing page\n");
break;
+ case AVIC_IPI_FAILURE_INVALID_IPI_VECTOR:
+ /* Invalid IPI with vector < 16 */
+ break;
default:
- pr_err("Unknown IPI interception\n");
+ WARN_ONCE(1, "Unknown avic incomplete IPI interception\n");
}

return 1;
--
2.26.3

2023-09-28 20:52:08

by Sean Christopherson

Subject: Re: [PATCH 2/5] x86: KVM: SVM: add support for Invalid IPI Vector interception

On Thu, Sep 28, 2023, Maxim Levitsky wrote:
> In later revisions of AMD's APM, there is a new 'incomplete IPI' exit code:
>
> "Invalid IPI Vector - The vector for the specified IPI was set to an
> illegal value (VEC < 16)"
>
> Note that tests on Zen2 machine show that this VM exit doesn't happen and
> instead AVIC just does nothing.
>
> Add support for this exit code by doing nothing, instead of filling
> the kernel log with errors.
>
> Also replace an unthrottled 'pr_err()' if another unknown incomplete
> IPI exit happens with WARN_ON_ONCE()
>
> (e.g in case AMD adds yet another 'Invalid IPI' exit reason)
>
> Cc: <[email protected]>
>
> Signed-off-by: Maxim Levitsky <[email protected]>
> ---
> arch/x86/include/asm/svm.h | 1 +
> arch/x86/kvm/svm/avic.c | 5 ++++-
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 19bf955b67e0da0..3ac0ffc4f3e202b 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -268,6 +268,7 @@ enum avic_ipi_failure_cause {
> AVIC_IPI_FAILURE_TARGET_NOT_RUNNING,
> AVIC_IPI_FAILURE_INVALID_TARGET,
> AVIC_IPI_FAILURE_INVALID_BACKING_PAGE,
> + AVIC_IPI_FAILURE_INVALID_IPI_VECTOR,
> };
>
> #define AVIC_PHYSICAL_MAX_INDEX_MASK GENMASK_ULL(8, 0)
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 2092db892d7d052..c44b65af494e3ff 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -529,8 +529,11 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
> case AVIC_IPI_FAILURE_INVALID_BACKING_PAGE:
> WARN_ONCE(1, "Invalid backing page\n");
> break;
> + case AVIC_IPI_FAILURE_INVALID_IPI_VECTOR:
> + /* Invalid IPI with vector < 16 */
> + break;
> default:
> - pr_err("Unknown IPI interception\n");
> + WARN_ONCE(1, "Unknown avic incomplete IPI interception\n");

Hrm, I'm not sure KVM should WARN here. E.g. if someone runs with panic_on_warn=1,
running on new hardware might crash the host. I hope that AMD is smart enough to
make any future failure types "optional" in the sense that they're either opt-in,
or are largely informational-only (like AVIC_IPI_FAILURE_INVALID_IPI_VECTOR).

I think switching to vcpu_unimpl(), or maybe even pr_err_once(), is more appropriate.