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| author |   Juergen Gross <jgross@suse.com> | 2021-01-20 14:55:45 +0100 |
|---|---|---|
| committer |   Borislav Petkov <bp@suse.de> | 2021-02-10 12:32:07 +0100 |
| commit | afd30525a659ac0ae0904f0cb4a2ca75522c3123 (patch) | |
| tree | ce45cda82fac21a848509aa29661353e634d45d6 /arch/x86/entry/entry_64.S | |
| parent | x86/pv: Switch SWAPGS to ALTERNATIVE (diff) | |
| download | wireguard-linux-afd30525a659ac0ae0904f0cb4a2ca75522c3123.tar.xz wireguard-linux-afd30525a659ac0ae0904f0cb4a2ca75522c3123.zip | |
x86/xen: Drop USERGS_SYSRET64 paravirt call
USERGS_SYSRET64 is used to return from a syscall via SYSRET, but
a Xen PV guest will nevertheless use the IRET hypercall, as there
is no sysret PV hypercall defined.
So instead of testing all the prerequisites for doing a sysret and
then mangling the stack for Xen PV again for doing an iret just use
the iret exit from the beginning.
This can easily be done via an ALTERNATIVE like it is done for the
sysenter compat case already.
It should be noted that this drops the optimization in Xen for not
restoring a few registers when returning to user mode, but it seems
as if the saved instructions in the kernel more than compensate for
this drop (a kernel build in a Xen PV guest was slightly faster with
this patch applied).
While at it remove the stale sysret32 remnants.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210120135555.32594-6-jgross@suse.com
Diffstat (limited to 'arch/x86/entry/entry_64.S')
| -rw-r--r-- | arch/x86/entry/entry_64.S | 16 |
1 files changed, 7 insertions, 9 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index a876204a73e0..ce0464d630a2 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -46,14 +46,6 @@ .code64 .section .entry.text, "ax" -#ifdef CONFIG_PARAVIRT_XXL -SYM_CODE_START(native_usergs_sysret64) - UNWIND_HINT_EMPTY - swapgs - sysretq -SYM_CODE_END(native_usergs_sysret64) -#endif /* CONFIG_PARAVIRT_XXL */ - /* * 64-bit SYSCALL instruction entry. Up to 6 arguments in registers. * @@ -123,7 +115,12 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL) * Try to use SYSRET instead of IRET if we're returning to * a completely clean 64-bit userspace context. If we're not, * go to the slow exit path. + * In the Xen PV case we must use iret anyway. */ + + ALTERNATIVE "", "jmp swapgs_restore_regs_and_return_to_usermode", \ + X86_FEATURE_XENPV + movq RCX(%rsp), %rcx movq RIP(%rsp), %r11 @@ -215,7 +212,8 @@ syscall_return_via_sysret: popq %rdi popq %rsp - USERGS_SYSRET64 + swapgs + sysretq SYM_CODE_END(entry_SYSCALL_64) /* |