Re: [PATCH Part2 v5 34/45] KVM: SVM: Do not use long-lived GHCB map while setting scratch area

[Sean Christopherson]

On Fri, Oct 15, 2021, Brijesh Singh wrote:
> 
> On 10/13/21 2:20 PM, Sean Christopherson wrote:
> > On Fri, Aug 20, 2021, Brijesh Singh wrote:
> >> The setup_vmgexit_scratch() function may rely on a long-lived GHCB
> >> mapping if the GHCB shared buffer area was used for the scratch area.
> >> In preparation for eliminating the long-lived GHCB mapping, always
> >> allocate a buffer for the scratch area so it can be accessed without
> >> the GHCB mapping.
> > Would it make sense to post this patch and the next (Remove the long-lived GHCB
> > host map) in a separate mini-series?  It's needed for SNP, but AFAICT there's
> > nothing that depends on SNP.  Getting this merged ahead of time would reduce the
> > size of the SNP series by a smidge.
> 
> While testing with random configs, I am seeing some might_sleep() warns.
> This is happening mainly because during the vmrun the GHCB is accessed
> with preempt disabled. The kvm_vcpu_map() -> kmap() reports the warning.
> I am leaning towards creating a cache on the vmgexit and use that cache
> instead of the doing a kmap() on every access. Does that sound okay to you ?

Since SEV is 64-bit only, it should be ok to add a kvm_vcpu_map_atomic() variant.