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

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Message-ID: <Yz+DRTfdFGmSR7Mq@google.com>
Date:   Fri, 7 Oct 2022 01:39:17 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Xu <peterx@...hat.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 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).