[PATCH] KVM: SVM: WARN, but continue, if misc_cg_set_capacity() fails

[PATCH] KVM: SVM: WARN, but continue, if misc_cg_set_capacity() fails

[Sean Christopherson]

WARN and continue if misc_cg_set_capacity() fails, as the only scenario
in which it can fail is if the specified resource is invalid, which should
never happen when CONFIG_KVM_AMD_SEV=y.  Deliberately not bailing "fixes"
a theoretical bug where KVM would leak the ASID bitmaps on failure, which
again can't happen.

If the impossible should happen, the end result is effectively the same
with respect to SEV and SEV-ES (they are unusable), while continuing on
has the advantage of letting KVM load, i.e. userspace can still run
non-SEV guests.

Reported-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/sev.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index d65578d8784d..07756b7348ae 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2216,9 +2216,7 @@ void __init sev_hardware_setup(void)
 	}
 
 	sev_asid_count = max_sev_asid - min_sev_asid + 1;
-	if (misc_cg_set_capacity(MISC_CG_RES_SEV, sev_asid_count))
-		goto out;
-
+	WARN_ON_ONCE(misc_cg_set_capacity(MISC_CG_RES_SEV, sev_asid_count));
 	sev_supported = true;
 
 	/* SEV-ES support requested? */
@@ -2243,9 +2241,7 @@ void __init sev_hardware_setup(void)
 		goto out;
 
 	sev_es_asid_count = min_sev_asid - 1;
-	if (misc_cg_set_capacity(MISC_CG_RES_SEV_ES, sev_es_asid_count))
-		goto out;
-
+	WARN_ON_ONCE(misc_cg_set_capacity(MISC_CG_RES_SEV_ES, sev_es_asid_count));
 	sev_es_supported = true;
 
 out:

base-commit: 6d1bc9754b04075d938b47cf7f7800814b8911a7
-- 
2.41.0.162.gfafddb0af9-goog

Re: [PATCH] KVM: SVM: WARN, but continue, if misc_cg_set_capacity() fails

[Sean Christopherson]

On Tue, 06 Jun 2023 17:44:49 -0700, Sean Christopherson wrote:
> WARN and continue if misc_cg_set_capacity() fails, as the only scenario
> in which it can fail is if the specified resource is invalid, which should
> never happen when CONFIG_KVM_AMD_SEV=y.  Deliberately not bailing "fixes"
> a theoretical bug where KVM would leak the ASID bitmaps on failure, which
> again can't happen.
> 
> If the impossible should happen, the end result is effectively the same
> with respect to SEV and SEV-ES (they are unusable), while continuing on
> has the advantage of letting KVM load, i.e. userspace can still run
> non-SEV guests.
> 
> [...]

Applied to kvm-x86 svm, thanks!

[1/1] KVM: SVM: WARN, but continue, if misc_cg_set_capacity() fails
      https://github.com/kvm-x86/linux/commit/106ed2cad9f7

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes