Re: [PATCH Part2 v5 05/45] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction

Brijesh Singh
2021-10-15T20:36:23Z

On 10/15/21 3:27 PM, Sean Christopherson wrote:
> On Fri, Oct 15, 2021, Brijesh Singh wrote:
>> On 10/15/21 1:05 PM, Sean Christopherson wrote:
>>> On Fri, Aug 20, 2021, Brijesh Singh wrote:
>>>> + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
>>> Shouldn't this be a WARN_ON_ONCE()?
>> Since some of these function are called while handling the PSC so I
>> tried to avoid using the WARN -- mainly because if the warn_on_panic=1
>> is set on the host then it will result in the kernel panic.
> But why would KVM be handling PSC requests if SNP is disabled?

The RMPUPDATE is also used by the CCP drv to change the page state
during the initialization. You are right that neither KVM nor CCP should
be using these function when SNP is not enabled. In your peudo code you
used the WARN_ON_ONCE() for the cpu_feature_enabled() and return code
check. I was more concern about the return code WARN_ON_ONCE() because
that will be called during the PSC. I am okay with using the
WARN_ON_ONCE() for the cpu_feature_enabled() check.

thanks