Re: [PATCH v2] x86/mce: fix wrong no-return-ip logic in do_machine_check()

From: Borislav Petkov <bp@alien8.de>
To: Aili Yao <yaoaili@kingsoft.com>
Cc: tony.luck@intel.com, mingo@redhat.com, tglx@linutronix.de,
	hpa@zytor.com, x86@kernel.org, linux-edac@vger.kernel.org,
	linux-kernel@vger.kernel.org, yangfeng1@kingsoft.com
Subject: Re: [PATCH v2] x86/mce: fix wrong no-return-ip logic in do_machine_check()
Date: Tue, 23 Feb 2021 10:43:00 +0100	[thread overview]
Message-ID: <20210223094300.GA26060@zn.tnic> (raw)
In-Reply-To: <20210223102755.13cbdffd@alex-virtual-machine>

On Tue, Feb 23, 2021 at 10:27:55AM +0800, Aili Yao wrote:
> When Guest access one address with UE error, it will exit guest mode,
> the host will do the recovery job, and then one SIGBUS is send to
> the VCPU and qemu will catch the signal, there is only address and
> error level no RIPV in signal, so qemu will assume RIPV is cleared and
> inject the error into guest OS.

Lemme see:

void kvm_arch_on_sigbus_vcpu(CPUState *c, int code, void *addr)

    /* If we get an action required MCE, it has been injected by KVM
     * while the VM was running.  An action optional MCE instead should
     * be coming from the main thread, which qemu_init_sigbus identifies
     * as the "early kill" thread.
     */
    assert(code == BUS_MCEERR_AR || code == BUS_MCEERR_AO);

    ...

	kvm_mce_inject(cpu, paddr, code);

in that function:

    if (code == BUS_MCEERR_AR) {
        status |= MCI_STATUS_AR | 0x134;
        mcg_status |= MCG_STATUS_EIPV;
    } else {
        status |= 0xc0;
        mcg_status |= MCG_STATUS_RIPV;
    }

That looks like a valid RIP bit to me. Then cpu_x86_inject_mce() gets
that mcg_status and injects it into the guest.

So I can't follow your claim - qemu does handle RIPV just fine, it
seems.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette