linux-kernel - Re: [PATCH v2] x86/mce: fix wrong no-return-ip logic in do_machine

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Message-ID: <20210224103921.3dcf0b65@alex-virtual-machine>
Date:   Wed, 24 Feb 2021 10:39:21 +0800
From:   Aili Yao <yaoaili@...gsoft.com>
To:     "Luck, Tony" <tony.luck@...el.com>
CC:     Borislav Petkov <bp@...en8.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yangfeng1@...gsoft.com" <yangfeng1@...gsoft.com>,
        <yaoaili@...gsoft.com>
Subject: Re: [PATCH v2] x86/mce: fix wrong no-return-ip logic in
 do_machine_check()

On Tue, 23 Feb 2021 16:12:43 +0000
"Luck, Tony" <tony.luck@...el.com> wrote:

> > What I think is qemu has not an easy to get the MCE signature from host or currently no methods for this
> > So qemu treat all AR will be No RIPV, Do more is better than do less.  
> 
> RIPV would be important in the guest in the case where the guest can fix the problem that caused
> the machine check and return to the failed instruction to continue.
> 
> I think the only case where this happens is a fault in a read-only page mapped from a file (typically
> code page, but could be a data page). In this case memory-failure() unmaps the page with the posion
> but Linux can recover by reading data from the file into a new page.
> 
> Other cases we send SIGBUS (so go to the signal handler instead of to the faulting instruction).
> 
> So it would be good if the state of RIPV could be added to the signal state sent to qemu. If that
> isn't possible, then this full recovery case turns into another SIGBUS case.

This KVM and VM case of failing recovery for SRAR is just one scenario I think,
If Intel guarantee that when memory SRAR is triggered, RIPV will always be set, then it's the job of qemu to
set the RIPV instead.
Or if When SRAR is triggered with RIPV cleared, the same issue will be true for host.

And I think it's better for VM to know the real RIPV value, It need more work in qemu and kernel if possible.

Thanks
Aili Yao