[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen stable-4.15] x86/spec-ctrl: Improve all SPEC_CTRL_{ENTER,EXIT}_* comments
commit 93504b3a6c92a1f2821af5e0960be8fda066ad77 Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> AuthorDate: Wed Aug 30 20:11:50 2023 +0100 Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CommitDate: Tue Sep 19 19:38:35 2023 +0100 x86/spec-ctrl: Improve all SPEC_CTRL_{ENTER,EXIT}_* comments ... to better explain how they're used. Doing so highlights that SPEC_CTRL_EXIT_TO_XEN is missing a VERW flush for the corner case when e.g. an NMI hits late in an exit-to-guest path. Leave a TODO, which will be addressed in subsequent patches which arrange for VERW flushing to be safe within SPEC_CTRL_EXIT_TO_XEN. Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> (cherry picked from commit 45f00557350dc7d0756551069803fc49c29184ca) --- xen/include/asm-x86/spec_ctrl_asm.h | 36 +++++++++++++++++++++++++++++++----- 1 file changed, 31 insertions(+), 5 deletions(-) diff --git a/xen/include/asm-x86/spec_ctrl_asm.h b/xen/include/asm-x86/spec_ctrl_asm.h index 1b4078ed8e..f8cd76fe9e 100644 --- a/xen/include/asm-x86/spec_ctrl_asm.h +++ b/xen/include/asm-x86/spec_ctrl_asm.h @@ -230,7 +230,10 @@ wrmsr .endm -/* Use after an entry from PV context (syscall/sysenter/int80/int82/etc). */ +/* + * Used after an entry from PV context: SYSCALL, SYSENTER, INT, + * etc. There is always a guest speculation state in context. + */ .macro SPEC_CTRL_ENTRY_FROM_PV /* * Requires %rsp=regs/cpuinfo, %rdx=0 @@ -245,7 +248,11 @@ X86_FEATURE_SC_MSR_PV .endm -/* Use in interrupt/exception context. May interrupt Xen or PV context. */ +/* + * Used after an exception or maskable interrupt, hitting Xen or PV context. + * There will either be a guest speculation context, or (barring fatal + * exceptions) a well-formed Xen speculation context. + */ .macro SPEC_CTRL_ENTRY_FROM_INTR /* * Requires %rsp=regs, %r14=stack_end, %rdx=0 @@ -260,7 +267,10 @@ X86_FEATURE_SC_MSR_PV .endm -/* Use when exiting to PV guest context. */ +/* + * Used when exiting from any entry context, back to PV context. This + * includes from an IST entry which moved onto the primary stack. + */ .macro SPEC_CTRL_EXIT_TO_PV /* * Requires %rax=spec_ctrl, %rsp=regs/info @@ -272,7 +282,13 @@ .endm /* - * Use in IST interrupt/exception context. May interrupt Xen or PV context. + * Used after an IST entry hitting Xen or PV context. Special care is needed, + * because when hitting Xen context, there may not be a well-formed + * speculation context. (i.e. it can hit in the middle of + * SPEC_CTRL_{ENTRY,EXIT}_* regions.) + * + * An IST entry which hits PV context moves onto the primary stack and leaves + * via SPEC_CTRL_EXIT_TO_PV, *not* SPEC_CTRL_EXIT_TO_XEN. */ .macro SPEC_CTRL_ENTRY_FROM_INTR_IST /* @@ -331,7 +347,14 @@ UNLIKELY_DISPATCH_LABEL(\@_serialise): UNLIKELY_END(\@_serialise) .endm -/* Use when exiting to Xen context. */ +/* + * Use when exiting from any entry context, back to Xen context. This + * includes returning to other SPEC_CTRL_{ENTRY,EXIT}_* regions with an + * incomplete speculation context. + * + * Because we might have interrupted Xen beyond SPEC_CTRL_EXIT_TO_$GUEST, we + * need to treat this as if it were an EXIT_TO_$GUEST case too. + */ .macro SPEC_CTRL_EXIT_TO_XEN /* * Requires %rbx=stack_end @@ -356,6 +379,9 @@ UNLIKELY_DISPATCH_LABEL(\@_serialise): wrmsr .L\@_skip_sc_msr: + + /* TODO VERW */ + .endm #endif /* __ASSEMBLY__ */ -- generated by git-patchbot for /home/xen/git/xen.git#stable-4.15
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