On Fri, May 14, 2021 at 01:38:53PM +0200, Jack Wang wrote:
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
>
> commit c5e2184d1544f9e56140791eff1a351bea2e63b9 upstream
>
> Remove the update_pte() shadow paging logic, which was obsoleted by
> commit 4731d4c7a077 ("KVM: MMU: out of sync shadow core"), but never
> removed. As pointed out by Yu, KVM never write protects leaf page
> tables for the purposes of shadow paging, and instead marks their
> associated shadow page as unsync so that the guest can write PTEs at
> will.
>
> The update_pte() path, which predates the unsync logic, optimizes COW
> scenarios by refreshing leaf SPTEs when they are written, as opposed to
> zapping the SPTE, restarting the guest, and installing the new SPTE on
> the subsequent fault. Since KVM no longer write-protects leaf page
> tables, update_pte() is unreachable and can be dropped.
>
> Reported-by: Yu Zhang <yu.c.zhang@xxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Message-Id: <20210115004051.4099250-1-seanjc@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> (jwang: backport to 5.4 to fix a warning on AMD nested Virtualization)
> Signed-off-by: Jack Wang <jinpu.wang@xxxxxxxxx>
> ---
> We hit a warning in WARNING: CPU: 62 PID: 29302 at arch/x86/kvm/mmu.c:2250 nonpaging_update_pte+0x5/0x10 [kvm]
> on AMD Opteron(tm) Processor 6386 SE with kernel 5.4.113, it seems nested L2 is running, I notice a similar bug
> report on https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1884058.
>
> I did test with kvm-unit-tests on both Intel Broadwell/Skylake, AMD Opteron, no
> regression, basic VM tests work fine too on 5.4 kernel.
> the commit c5e2184d1544f9e56140791eff1a351bea2e63b9 can be cherry-picked cleanly
> to kernel 5.10+.
Now queued up, thanks.
greg k-h
