| Message ID | 20230913202758.508225-6-andrew.cooper3@citrix.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | x86/spec-ctrl: AMD DIV fix, and VERW prerequisite bugfixes | expand |
On 13.09.2023 22:27, Andrew Cooper wrote: > All other SPEC_CTRL_{ENTRY,EXIT}_* helpers hold stack_end in %r14. Adjust it > for consistency, freeing up %rbx to be used differently. > > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com> The choice of %rbx was, iirc, for avoiding unnecessary code size increase (due to extra REX prefixes needed in some of the affected insns). I understand you view this as not a real concern, but I think saying so explicitly in the description would be at least desirable. After all there would also be the alternative of further parametrizing the involved macros. Jan
On 14/09/2023 9:51 am, Jan Beulich wrote: > On 13.09.2023 22:27, Andrew Cooper wrote: >> All other SPEC_CTRL_{ENTRY,EXIT}_* helpers hold stack_end in %r14. Adjust it >> for consistency, freeing up %rbx to be used differently. >> >> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> > Reviewed-by: Jan Beulich <jbeulich@suse.com> > > The choice of %rbx was, iirc, for avoiding unnecessary code size increase > (due to extra REX prefixes needed in some of the affected insns). I > understand you view this as not a real concern, but I think saying so > explicitly in the description would be at least desirable. After all there > would also be the alternative of further parametrizing the involved macros. Yeah I'm seriously not concerned about a REX prefix or two. This is about making all the helpers more consistent, to cut down on the number of errors involved in modifying this mess. ~Andrew
diff --git a/xen/arch/x86/include/asm/spec_ctrl_asm.h b/xen/arch/x86/include/asm/spec_ctrl_asm.h index 77f6c35bb9c5..acdb526d292d 100644 --- a/xen/arch/x86/include/asm/spec_ctrl_asm.h +++ b/xen/arch/x86/include/asm/spec_ctrl_asm.h @@ -344,10 +344,10 @@ UNLIKELY_DISPATCH_LABEL(\@_serialise): */ .macro SPEC_CTRL_EXIT_TO_XEN /* - * Requires %rbx=stack_end + * Requires %r14=stack_end * Clobbers %rax, %rcx, %rdx */ - testb $SCF_ist_sc_msr, STACK_CPUINFO_FIELD(spec_ctrl_flags)(%rbx) + testb $SCF_ist_sc_msr, STACK_CPUINFO_FIELD(spec_ctrl_flags)(%r14) jz .L\@_skip_sc_msr /* @@ -358,10 +358,10 @@ UNLIKELY_DISPATCH_LABEL(\@_serialise): */ xor %edx, %edx - testb $SCF_use_shadow, STACK_CPUINFO_FIELD(spec_ctrl_flags)(%rbx) + testb $SCF_use_shadow, STACK_CPUINFO_FIELD(spec_ctrl_flags)(%r14) jz .L\@_skip_sc_msr - mov STACK_CPUINFO_FIELD(shadow_spec_ctrl)(%rbx), %eax + mov STACK_CPUINFO_FIELD(shadow_spec_ctrl)(%r14), %eax mov $MSR_SPEC_CTRL, %ecx wrmsr diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S index a1c860f56949..525877e97330 100644 --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -665,15 +665,15 @@ restore_all_xen: * Check whether we need to switch to the per-CPU page tables, in * case we return to late PV exit code (from an NMI or #MC). */ - GET_STACK_END(bx) - cmpb $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%rbx) + GET_STACK_END(14) + cmpb $0, STACK_CPUINFO_FIELD(use_pv_cr3)(%r14) UNLIKELY_START(ne, exit_cr3) - mov STACK_CPUINFO_FIELD(pv_cr3)(%rbx), %rax + mov STACK_CPUINFO_FIELD(pv_cr3)(%r14), %rax mov %rax, %cr3 UNLIKELY_END(exit_cr3) /* WARNING! `ret`, `call *`, `jmp *` not safe beyond this point. */ - SPEC_CTRL_EXIT_TO_XEN /* Req: %rbx=end, Clob: acd */ + SPEC_CTRL_EXIT_TO_XEN /* Req: %r14=end, Clob: acd */ RESTORE_ALL adj=8 iretq
All other SPEC_CTRL_{ENTRY,EXIT}_* helpers hold stack_end in %r14. Adjust it for consistency, freeing up %rbx to be used differently. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: Jan Beulich <JBeulich@suse.com> CC: Roger Pau Monné <roger.pau@citrix.com> CC: Wei Liu <wl@xen.org> --- xen/arch/x86/include/asm/spec_ctrl_asm.h | 8 ++++---- xen/arch/x86/x86_64/entry.S | 8 ++++---- 2 files changed, 8 insertions(+), 8 deletions(-)