linux-kernel - Re: [PATCH] x86/mce: Check that memory address is usable for recovery

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Date:   Tue, 18 Apr 2023 11:23:58 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Yazen Ghannam <yazen.ghannam@....com>
Cc:     Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH] x86/mce: Check that memory address is usable for recovery

On Tue, Apr 18, 2023 at 01:51:37PM -0400, Yazen Ghannam wrote:
> I agree. And I think all these checks should be baked into the severity.
> We'll need additional, fine-grained severity levels though.
> 
> The "m.cs" and "m.kflags" checks could also be baked in.
> 
> Instead of just one AR severity:
> 	...
> 	MCE_AR_SEVERITY,
> 	MCE_PANIC_SEVERITY,
> 
> replace it with specific cases:
> 	...
> 	MCE_AR_USER_RECOV,
> 	MCE_AR_USER_KILL,
> 	MCE_AR_KERNEL_COPYIN,
> 	MCE_AR_KERNEL_RECOV,
> 	MCE_PANIC_SEVERITY,
> 
> Then the #MC handler can look like this:
> 
> 	if (worst < MCE_AR_USER_RECOV)
> 		goto out;
> 
> 	if (severity == MCE_AR_USER_RECOV)
> 		queue_task_work(&m, msg, kill_me_maybe);
> 
> 	if (severity == MCE_AR_USER_KILL)
> 		force_sig(SIGBUS);
> 
> 	if (severity == MCE_AR_KERNEL_COPYIN)
> 		queue_task_work(&m, msg, kill_me_never);
> 	
> 	if (severity == MCE_AR_KERNEL_RECOV) {
> 		if (!fixup_exception(regs, X86_TRAP_MC, 0, 0))
> 			mce_panic("Failed kernel mode recovery");
> 	}
> 
> I can take a shot at this if it seems reasonable.

That looks much cleaner. There may be some extra MCE_AR_KERNEL* options
in the future (I'd like someday to address COPYOUT when the corrupt
kernel data is in the page cache). But I don't think the number of cases
is going to explode into dozens of cases.

> What do you think?

Brave person ... you are going to have to tinker with
arch/x86/kernel/cpu/mce/severity.c !  Good luck.

-Tony