On Nov 14, 2020, at 10:33 PM, Jürgen Groß <jgross@xxxxxxxx> wrote:
On 14.11.20 19:10, Andy Lutomirski wrote:
On Sat, Nov 14, 2020 at 1:16 AM Jürgen Groß <jgross@xxxxxxxx> wrote:ALTERNATIVE would "work" in the sense that it would function and be
On 13.11.20 18:34, Andy Lutomirski wrote:
On Wed, Nov 11, 2020 at 12:25 PM Andrew Cooper
<andrew.cooper3@xxxxxxxxxx> 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.
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 :)
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