linux-kernel - RE: [PATCH v3] x86/fault: Send a SIGBUS to user process always for hwpoison page access.

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Date:   Mon, 8 Mar 2021 18:31:07 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Andy Lutomirski <luto@...capital.net>,
        Aili Yao <yaoaili@...gsoft.com>
CC:     Andy Lutomirski <luto@...nel.org>,
        HORIGUCHI NAOYA <naoya.horiguchi@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        "yangfeng1@...gsoft.com" <yangfeng1@...gsoft.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3] x86/fault: Send a SIGBUS to user process always for
 hwpoison page access.

> Can you point me at that SIGBUS code in a current kernel?

It is in kill_me_maybe().  mce_vaddr is setup when we disassemble whatever get_user()
or copy from user variant was in use in the kernel when the poison memory was consumed.

        if (p->mce_vaddr != (void __user *)-1l) {
                force_sig_mceerr(BUS_MCEERR_AR, p->mce_vaddr, PAGE_SHIFT);

Would it be any better if we used the BUS_MCEERR_AO code that goes into siginfo?

That would make it match up better with what happens when poison is found
asynchronously by the patrol scrubber. I.e. the semantics are:

AR: You just touched poison at this address and need to do something about that.
AO: Just letting you know that you have some poison at the address in siginfo.

-Tony