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    SubjectRe: [PATCH V2 0/4] x86/entry: simply stack switching when exception on userspace
    On Sat, May 30, 2020 at 2:33 AM Andy Lutomirski <luto@kernel.org> wrote:
    >
    > On Fri, May 29, 2020 at 1:26 AM Lai Jiangshan <laijs@linux.alibaba.com> 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

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