linux-kernel - Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

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Date:   Fri, 12 Mar 2021 13:55:31 +0800
From:   Aili Yao <yaoaili@...gsoft.com>
To:     "Luck, Tony" <tony.luck@...el.com>
CC:     "HORIGUCHI NAOYA堀口　直也)" 
        <naoya.horiguchi@....com>, Oscar Salvador <osalvador@...e.de>,
        "david@...hat.com" <david@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "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>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "yangfeng1@...gsoft.com" <yangfeng1@...gsoft.com>,
        <yaoaili@...gsoft.com>, <sunhao2@...gsoft.com>
Subject: Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

On Thu, 11 Mar 2021 17:05:53 +0000
"Luck, Tony" <tony.luck@...el.com> wrote:

> > I guess that p->mce_vaddr stores the virtual address of the error here.
> > If so, sending SIGBUS with the address looks enough as we do now, so why
> > do you walk page table to find the error virtual address?  
> 
> p->mce_vaddr only has the virtual address for the COPYIN case. In that code
> path we decode the kernel instruction that hit the fault in order to find the virtual
> address. That's easy because:
> 
> 1) The kernel RIP is known to be good (can't page fault etc. on kernel address).
> 2) There are only a half dozen instructions used by the kernel for get_user() or
>      copy_from_user().
> 
> When the machine check happens during user execution accessing poison data
> we only have the physical address (from MCi_ADDR).
> 
> -Tony

Sorry to interrupt as I am really confused here:
If it's a copyin case, has the page been mapped for the current process?
will memory_failure() find it and unmap it? if succeed, then the current will be
signaled with correct vaddr and shift?

Maybe the mce_vaddr is set correctly, but we may lost the correct page shift?

And for copyin case, we don't need to call set_mce_nospec()?

-- 
Thanks!
Aili Yao