linux-kernel - Re: [PATCH v13 09/35] KVM: Add KVM_EXIT_MEMORY_FAULT exit to report faults to userspace

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Message-ID: <496b78bb-ad12-4eed-a62c-8c2fd725ec61@redhat.com>
Date:   Thu, 2 Nov 2023 12:03:39 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Huang, Kai" <kai.huang@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Cc:     "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        "kvm-riscv@...ts.infradead.org" <kvm-riscv@...ts.infradead.org>,
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Subject: Re: [PATCH v13 09/35] KVM: Add KVM_EXIT_MEMORY_FAULT exit to report
 faults to userspace

On 11/2/23 10:35, Huang, Kai wrote:
> IIUC KVM can already handle the case of poisoned
> page by sending signal to user app: 
> 
> 	static int kvm_handle_error_pfn(struct kvm_vcpu *vcpu, 
> 			struct kvm_page_fault *fault)                                               
> 	{       
> 		...
> 
>        		if (fault->pfn == KVM_PFN_ERR_HWPOISON) {
>               		kvm_send_hwpoison_signal(fault->slot, fault->gfn);
>                 	return RET_PF_RETRY;                                          
>         	}
> 	}

EHWPOISON is not implemented by this series, so it should be left out of 
the documentation.


> Currently as mentioned above when
> vepc fault handler cannot allocate EPC page KVM returns -EFAULT to Qemu, and
> Qemu prints ...
> 
> 	...: Bad address
> 	<dump guest cpu registers>
> 
> ... which is nonsense.
> 
> If we can use memory_fault.flags (or is 'fault_reason' a better name?) to carry
> a specific value for EPC to let Qemu know and Qemu can then do more reasonable
> things.

Yes, that's a good idea that can be implemented on top.

Paolo