Re: [PATCH v2 01/26] KVM: x86/mmu: Optimize MMU page cache lookup for all direct SPs

Peter Xu
2022-03-15T07:40:33Z

On Fri, Mar 11, 2022 at 12:25:03AM +0000, David Matlack wrote:
> Commit fb58a9c345f6 ("KVM: x86/mmu: Optimize MMU page cache lookup for
> fully direct MMUs") skipped the unsync checks and write flood clearing
> for full direct MMUs. We can extend this further and skip the checks for
> all direct shadow pages. Direct shadow pages are never marked unsynced
> or have a non-zero write-flooding count.

Nit: IMHO it's better to spell out the exact functional change, IIUC those
are the direct mapped SPs where guest uses huge pages but host uses only
small pages for the shadowing?

>
> Checking sp->role.direct alos generates better code than checking
> direct_map because, due to register pressure, direct_map has to get
> shoved onto the stack and then pulled back off.
>
> No functional change intended.
>
> Reviewed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

--
Peter Xu