[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging-4.13] x86/spec-ctrl: Rework SPEC_CTRL_ENTRY_FROM_INTR_IST
commit 5994b739453fa36d8724f3b06dc10884ca69427f Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> AuthorDate: Fri Jul 1 15:59:40 2022 +0100 Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CommitDate: Tue Jul 12 16:33:19 2022 +0100 x86/spec-ctrl: Rework SPEC_CTRL_ENTRY_FROM_INTR_IST We are shortly going to add a conditional IBPB in this path. Therefore, we cannot hold spec_ctrl_flags in %eax, and rely on only clobbering it after we're done with its contents. %rbx is available for use, and the more normal register to hold preserved information in. With %rax freed up, use it instead of %rdx for the RSB tmp register, and for the adjustment to spec_ctrl_flags. This leaves no use of %rdx, except as 0 for the upper half of WRMSR. In practice, %rdx is 0 from SAVE_ALL on all paths and isn't likely to change in the foreseeable future, so update the macro entry requirements to state this dependency. This marginal optimisation can be revisited if circumstances change. No practical change. This is part of XSA-407. Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> (cherry picked from commit e9b8d31981f184c6539f91ec54bd9cae29cdae36) --- xen/arch/x86/x86_64/entry.S | 4 ++-- xen/include/asm-x86/spec_ctrl_asm.h | 21 ++++++++++----------- 2 files changed, 12 insertions(+), 13 deletions(-) diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S index 6a5f8aaec3..481110fb93 100644 --- a/xen/arch/x86/x86_64/entry.S +++ b/xen/arch/x86/x86_64/entry.S @@ -805,7 +805,7 @@ ENTRY(double_fault) GET_STACK_END(14) - SPEC_CTRL_ENTRY_FROM_INTR_IST /* Req: %rsp=regs, %r14=end, Clob: acd */ + SPEC_CTRL_ENTRY_FROM_INTR_IST /* Req: %rsp=regs, %r14=end, %rdx=0, Clob: abcd */ /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */ mov STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rbx @@ -838,7 +838,7 @@ handle_ist_exception: GET_STACK_END(14) - SPEC_CTRL_ENTRY_FROM_INTR_IST /* Req: %rsp=regs, %r14=end, Clob: acd */ + SPEC_CTRL_ENTRY_FROM_INTR_IST /* Req: %rsp=regs, %r14=end, %rdx=0, Clob: abcd */ /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */ mov STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rcx diff --git a/xen/include/asm-x86/spec_ctrl_asm.h b/xen/include/asm-x86/spec_ctrl_asm.h index 3e9d6bd114..3ec680b587 100644 --- a/xen/include/asm-x86/spec_ctrl_asm.h +++ b/xen/include/asm-x86/spec_ctrl_asm.h @@ -258,34 +258,33 @@ */ .macro SPEC_CTRL_ENTRY_FROM_INTR_IST /* - * Requires %rsp=regs, %r14=stack_end - * Clobbers %rax, %rcx, %rdx + * Requires %rsp=regs, %r14=stack_end, %rdx=0 + * Clobbers %rax, %rbx, %rcx, %rdx * * This is logical merge of DO_OVERWRITE_RSB and DO_SPEC_CTRL_ENTRY * maybexen=1, but with conditionals rather than alternatives. */ - movzbl STACK_CPUINFO_FIELD(spec_ctrl_flags)(%r14), %eax + movzbl STACK_CPUINFO_FIELD(spec_ctrl_flags)(%r14), %ebx - test $SCF_ist_rsb, %al + test $SCF_ist_rsb, %bl jz .L\@_skip_rsb - DO_OVERWRITE_RSB tmp=rdx /* Clobbers %rcx/%rdx */ + DO_OVERWRITE_RSB /* Clobbers %rax/%rcx */ .L\@_skip_rsb: - test $SCF_ist_sc_msr, %al + test $SCF_ist_sc_msr, %bl jz .L\@_skip_msr_spec_ctrl - xor %edx, %edx + xor %eax, %eax testb $3, UREGS_cs(%rsp) - setnz %dl - not %edx - and %dl, STACK_CPUINFO_FIELD(spec_ctrl_flags)(%r14) + setnz %al + not %eax + and %al, STACK_CPUINFO_FIELD(spec_ctrl_flags)(%r14) /* Load Xen's intended value. */ mov $MSR_SPEC_CTRL, %ecx movzbl STACK_CPUINFO_FIELD(xen_spec_ctrl)(%r14), %eax - xor %edx, %edx wrmsr /* Opencoded UNLIKELY_START() with no condition. */ -- generated by git-patchbot for /home/xen/git/xen.git#staging-4.13
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