Re: [RFC PATCH] x86, entry: Switch stacks on a paranoid entry from userspace

From: Andy Lutomirski
Date: Mon Nov 17 2014 - 15:06:25 EST

On Mon, Nov 17, 2014 at 12:03 PM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Mon, Nov 17, 2014 at 11:57:22AM -0800, Andy Lutomirski wrote:
>> Would it be worth making a decision on task_work_add vs. stack
>> switching first?
> Probably a prudent thing to do in order to save unnecessary cycles :-)
>> Stack switching pros: all this lockless allocation stuff is completely
>> unnecessary, and it's plausible that the stack switching code will be
>> added anyway.
> Yes.
> However, I'd like to be very sure this thing doesn't introduce any
> regressions to the MCA code. So even if Tony's testing passes, I'd like
> to be very conservative here and stress it more than usual. Because once
> this thing hits upstream and stuff starts breaking, it'll be a serious
> PITA reverting it.
> I hope you can understand my concerns.

I agree completely.

> Btw, which branch has your latest version - I'd like to take a look at
> it in detail.

I'm not quite ready to send v3. I want to do two things first:

1. Consider disabling the stack switch for double_fault.

2. Clean up the macros. I'll validate this by ensuring that the
generated code is identical to the current version.

IOW, I don't expect the asm for machine_check to change.

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