linux-kernel - Re: [PATCH 2/2] KVM, Fix QEMU-KVM is killed by guest SRAO MCE

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Date:	Wed, 28 Apr 2010 10:56:15 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"masbock@...ux.vnet.ibm.com" <masbock@...ux.vnet.ibm.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH 2/2] KVM, Fix QEMU-KVM is killed by guest SRAO MCE

On Tue, 2010-04-27 at 17:30 +0800, Avi Kivity wrote:
> On 04/27/2010 12:25 PM, Huang Ying wrote:
> >
> >
> >> On 04/27/2010 10:04 AM, Huang Ying wrote:
> >>      
> >>> +static void kvm_send_hwpoison_signal(struct kvm *kvm, gfn_t gfn)
> >>> +{
> >>> +	char buf[1];
> >>> +	void __user *hva;
> >>> +	int r;
> >>> +
> >>> +	/* Touch the page, so send SIGBUS */
> >>> +	hva = (void __user *)gfn_to_hva(kvm, gfn);
> >>> +	r = copy_from_user(buf, hva, 1);
> >>>
> >>>        
> >> No error check?  What will a copy_from_user() of poisoned page expected
> >> to return?
> >>
> >> Best to return -EFAULT on failure for consistency.
> >>      
> > Just want to use the side effect of copy_from_user, SIGBUS will be sent
> > to current process because the page touched is marked as poisoned. That
> > is, failure is expected, so the return value is not checked.
> >    
> 
> What if the failure doesn't happen?  Say, someone mmap()ed over the page.

Sorry, not get your idea clearly. hva is re-mmap()ed? We just read the
hva, not write, so I think it should be OK here.

> btw, better to use (void)copy_from_user(...) instead to avoid the 
> initialized but not used warning the compiler may generate.

OK. Will do that.

Best Regards,
Huang Ying


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