On Mon, Nov 16, 2020 at 7:23 AM Juergen Gross <jgross@xxxxxxxx> wrote: > > 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. > > While at it remove to stale sysret32 remnants. > > Signed-off-by: Juergen Gross <jgross@xxxxxxxx> Acked-by: Andy Lutomirski <luto@xxxxxxxxxx> FWIW, you've lost the VGCF_in_syscall optimization. Let me see if I can give it back to you better. > --- > arch/x86/entry/entry_64.S | 22 +++++++++------------- > arch/x86/include/asm/irqflags.h | 6 ------ > arch/x86/include/asm/paravirt.h | 5 ----- > arch/x86/include/asm/paravirt_types.h | 8 -------- > arch/x86/kernel/asm-offsets_64.c | 2 -- > arch/x86/kernel/paravirt.c | 5 +---- > arch/x86/kernel/paravirt_patch.c | 4 ---- > arch/x86/xen/enlighten_pv.c | 1 - > arch/x86/xen/xen-asm.S | 20 -------------------- > arch/x86/xen/xen-ops.h | 2 -- > 10 files changed, 10 insertions(+), 65 deletions(-) > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > index a876204a73e0..df865eebd3d7 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. > * > @@ -123,12 +115,15 @@ 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. > */ > - movq RCX(%rsp), %rcx > - movq RIP(%rsp), %r11 > > - cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */ > - jne swapgs_restore_regs_and_return_to_usermode > + ALTERNATIVE __stringify( \ > + movq RCX(%rsp), %rcx; \ > + movq RIP(%rsp), %r11; \ > + cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \ > + jne swapgs_restore_regs_and_return_to_usermode), \ > + "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV I'm not in love with this save-a-few-bytes stringify, but I can live with it. --Andy _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
