linux-kernel - Re: [PATCH v3 2/3] kvm: Add new pfn error KVM_PFN_ERR

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Date:   Fri, 7 Oct 2022 11:03:41 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Linux MM Mailing List <linux-mm@...ck.org>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v3 2/3] kvm: Add new pfn error KVM_PFN_ERR_SIGPENDING

On Fri, Oct 07, 2022 at 01:39:17AM +0000, Sean Christopherson wrote:
> On Tue, Aug 16, 2022, Peter Xu wrote:
> > Since at it, renaming kvm_handle_bad_page to kvm_handle_error_pfn assuming
> 
> Please put parantheses after function names, e.g. kvm_handle_bad_page().
> 
> > that'll match better with what it does, e.g. KVM_PFN_ERR_SIGPENDING is not
> > accurately a bad page but just one kind of errors.
> 
> ...
> 
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 3e1317325e1f..23dc46da2f18 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3134,8 +3134,13 @@ static void kvm_send_hwpoison_signal(unsigned long address, struct task_struct *
> >  	send_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, PAGE_SHIFT, tsk);
> >  }
> >  
> > -static int kvm_handle_bad_page(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn)
> > +static int kvm_handle_error_pfn(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn)
> >  {
> > +	if (is_sigpending_pfn(pfn)) {
> > +		kvm_handle_signal_exit(vcpu);
> > +		return -EINTR;
> > +	}
> 
> ...
> 
> > @@ -2648,9 +2651,12 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
> >  	if (atomic)
> >  		return KVM_PFN_ERR_FAULT;
> >  
> > -	npages = hva_to_pfn_slow(addr, async, write_fault, writable, &pfn);
> > +	npages = hva_to_pfn_slow(addr, async, write_fault, interruptible,
> > +				 writable, &pfn);
> >  	if (npages == 1)
> >  		return pfn;
> > +	if (npages == -EINTR)
> > +		return KVM_PFN_ERR_SIGPENDING;
> 
> This patch should be split into 3 parts:
> 
>   1. Add KVM_PFN_ERR_SIGPENDING and the above code
>   2. Add the interruptible flag
>   3. Add handling in x86 and rename kvm_handle_bad_page()
> 
> With #3 merged with patch 3.
> 
> That was if there's oddball arch code that reacts poorly to KVM_PFN_ERR_SIGPENDING,
> those errors will bisect to #1.
> 
> And if there's a typo in the plumbing, that bisects to #2.
> 
> And if something goes sideways in x86, those bugs bisect to #3 (patch 3), and it's
> easy to revert just the x86 changes (though I can't imagine that's likely).

Yeah the x86 change in this patch is indeed a bit weird with the generic
subject.  All points taken, thanks.

-- 
Peter Xu