Re: [PATCH V2 0/4] x86/entry: simply stack switching when exception on userspace

[Lai Jiangshan]

On Sat, May 30, 2020 at 2:33 AM Andy Lutomirski <luto@xxxxxxxxxx> wrote:
>
> On Fri, May 29, 2020 at 1:26 AM Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx> wrote:
> >
> > 7f2590a110b8("x86/entry/64: Use a per-CPU trampoline stack for IDT entries")
> > has resulted that when exception on userspace, the kernel (error_entry)
> > always push the pt_regs to entry stack(sp0), and then copy them to the
> > kernel stack.
> >
> > And recent x86/entry work makes interrupt also use idtentry
> > and makes all the interrupt code save the pt_regs on the sp0 stack
> > and then copy it to the thread stack like exception.
> >
> > This is hot path (page fault, ipi), such overhead should be avoided.
> > And the original interrupt_entry directly switches to kernel stack
> > and pushes pt_regs to kernel stack. We should do it for error_entry.
> > This is the job of patch1.
> >
> > Patch 2-4 simply stack switching for .Lerror_bad_iret by just doing
> > all the work in one function (fixup_bad_iret()).
> >
> > The patch set is based on tip/x86/entry (28447ea41542) (May 20).
>
> There are definitely good cleanups in here, but I think it would be
> nice rebased to whatever lands in 5.8-rc1 settles.
>

Hello, All

This patchset can be smoothly applicable to the newest tip/x86/entry
which has 5.8-rc1 merged. Which means I don't have to respin/resend it
until any update is needed.

Could you have a review on it please.

Thanks
Lai