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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@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com>
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Andrew Cooper committed
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+31
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@@ -218,7 +218,10 @@
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wrmsr
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.endm
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/* Use after an entry from PV context (syscall/sysenter/int80/int82/etc). */
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/*
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* Used after an entry from PV context: SYSCALL, SYSENTER, INT,
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* etc. There is always a guest speculation state in context.
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*/
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.macro SPEC_CTRL_ENTRY_FROM_PV
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/*
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* Requires %rsp=regs/cpuinfo, %rdx=0
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@@ -233,7 +236,11 @@
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X86_FEATURE_SC_MSR_PV
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.endm
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/* Use in interrupt/exception context. May interrupt Xen or PV context. */
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/*
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* Used after an exception or maskable interrupt, hitting Xen or PV context.
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* There will either be a guest speculation context, or (barring fatal
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* exceptions) a well-formed Xen speculation context.
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*/
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.macro SPEC_CTRL_ENTRY_FROM_INTR
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/*
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* Requires %rsp=regs, %r14=stack_end, %rdx=0
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@@ -248,7 +255,10 @@
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X86_FEATURE_SC_MSR_PV
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.endm
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/* Use when exiting to PV guest context. */
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/*
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* Used when exiting from any entry context, back to PV context. This
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* includes from an IST entry which moved onto the primary stack.
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*/
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.macro SPEC_CTRL_EXIT_TO_PV
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/*
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* Requires %rax=spec_ctrl, %rsp=regs/info
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@@ -260,7 +270,13 @@
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.endm
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/*
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* Use in IST interrupt/exception context. May interrupt Xen or PV context.
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* Used after an IST entry hitting Xen or PV context. Special care is needed,
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* because when hitting Xen context, there may not be a well-formed
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* speculation context. (i.e. it can hit in the middle of
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* SPEC_CTRL_{ENTRY,EXIT}_* regions.)
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*
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* An IST entry which hits PV context moves onto the primary stack and leaves
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* via SPEC_CTRL_EXIT_TO_PV, *not* SPEC_CTRL_EXIT_TO_XEN.
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*/
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.macro SPEC_CTRL_ENTRY_FROM_INTR_IST
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/*
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@@ -319,7 +335,14 @@ UNLIKELY_DISPATCH_LABEL(\@_serialise):
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UNLIKELY_END(\@_serialise)
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.endm
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/* Use when exiting to Xen context. */
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/*
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* Use when exiting from any entry context, back to Xen context. This
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* includes returning to other SPEC_CTRL_{ENTRY,EXIT}_* regions with an
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* incomplete speculation context.
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*
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* Because we might have interrupted Xen beyond SPEC_CTRL_EXIT_TO_$GUEST, we
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* need to treat this as if it were an EXIT_TO_$GUEST case too.
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*/
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.macro SPEC_CTRL_EXIT_TO_XEN
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/*
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* Requires %rbx=stack_end
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@@ -344,6 +367,9 @@ UNLIKELY_DISPATCH_LABEL(\@_serialise):
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wrmsr
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.L\@_skip_sc_msr:
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/* TODO VERW */
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.endm
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#endif /* __ASSEMBLY__ */
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