linux-kernel - Re: [PATCH v2 3/3] kvm/x86: Allow to respond to generic signals during slow page faults

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Date:   Tue, 16 Aug 2022 15:51:16 -0700
From:   David Matlack <dmatlack@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Linux MM Mailing List <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH v2 3/3] kvm/x86: Allow to respond to generic signals
 during slow page faults

On Tue, Aug 16, 2022 at 1:48 PM Peter Xu <peterx@...hat.com> wrote:
>
> On Mon, Aug 15, 2022 at 09:26:37PM +0000, Sean Christopherson wrote:
> > On Thu, Aug 11, 2022, Peter Xu wrote:
> > > On Thu, Aug 11, 2022 at 08:12:38PM +0000, Sean Christopherson wrote:
> > > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > > > index 17252f39bd7c..aeafe0e9cfbf 100644
> > > > > --- a/arch/x86/kvm/mmu/mmu.c
> > > > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > > > @@ -3012,6 +3012,13 @@ static int kvm_handle_bad_page(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn)
> > > > >  static int handle_abnormal_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
> > > > >                                unsigned int access)
> > > > >  {
> > > > > +       /* NOTE: not all error pfn is fatal; handle sigpending pfn first */
> > > > > +       if (unlikely(is_sigpending_pfn(fault->pfn))) {
> > > >
> > > > Move this into kvm_handle_bad_page(), then there's no need for a comment to call
> > > > out that this needs to come before the is_error_pfn() check.  This _is_ a "bad"
> > > > PFN, it just so happens that userspace might be able to resolve the "bad" PFN.
> > >
> > > It's a pity it needs to be in "bad pfn" category since that's the only
> > > thing we can easily use, but true it is now.
> >
> > Would renaming that to kvm_handle_error_pfn() help?  I agree that "bad" is poor
> > terminology now that it handles a variety of errors, hence the quotes.
>
> It could be slightly helpful I think, at least it starts to match with how
> we name KVM_PFN_ERR_*.  Will squash the renaming into the same patch.

+1 to kvm_handle_error_pfn(). Weirdly I proposed the same as part of
another series  yesterday [1]. That being said I'm probably going to
drop my cleanup patch (specifically patches 7-9) since it conflicts
with your changes and there is a bug in the last patch.

[1] https://lore.kernel.org/kvm/20220815230110.2266741-8-dmatlack@google.com/

>
> Thanks,
>
> --
> Peter Xu
>