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SubjectRe: WARNING: can't access registers at asm_common_interrupt
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> On Nov 14, 2020, at 10:33 PM, Jürgen Groß <jgross@suse.com> wrote:
>
> On 14.11.20 19:10, Andy Lutomirski wrote:
>>> On Sat, Nov 14, 2020 at 1:16 AM Jürgen Groß <jgross@suse.com> wrote:
>>>
>>> On 13.11.20 18:34, Andy Lutomirski wrote:
>>>> On Wed, Nov 11, 2020 at 12:25 PM Andrew Cooper
>>>> <andrew.cooper3@citrix.com> wrote:
>>>>
>>>> So I think there is at most one of these that wants anything more
>>>> complicated than a plain ALTERNATIVE. Any volunteers to make it so?
>>>> Juergen, if you do all of them except USERGS_SYSRET64, I hereby
>>>> volunteer to do that one.
>>>
>>> Why is a plain alternative (either swapgs; sysretq or a jmp xen_sysret64
>>> depending on X86_FEATURE_XENPV) no option?
>>>
>>> Its not as if this code would run before alternative patching.
>> ALTERNATIVE would "work" in the sense that it would function and be
>> just about as nonsensical as the current code. Fundamentally, Xen
>> PV's sysret feature is not a drop-in replacement for SYSRET64, and
>> pretending that it is seems unlikely to work well. I suspect that the
>> current code is some combination of exceedingly slow, non-functional,
>> and incorrect in subtle ways.
>> We should just have a separate Xen PV exit path the same way we have a
>> separate entry path in recent kernels. *This* is what I'm
>> volunteering to do.
>
> I don't think there is much work needed. Xen PV does basically a return
> to user mode via IRET. I think it might work just to use
> swapgs_restore_regs_and_return_to_usermode() unconditionally for Xen PV.
>

I’m quite confident that will work, but I was hoping to get it to work quickly too :)

>
> Juergen
> <OpenPGP_0xB0DE9DD628BF132F.asc>

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