[PATCH 3/3] x86/sev-es: Improve comments in and around __sev_es_ist_enter/exit()
STALE2053d
From: Joerg Roedel <joro@8bytes.org>
Date: 2021-02-17 12:08:08
Also in:
kvm, lkml
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
From: Joerg Roedel <redacted> Better explain why this code is necessary and what it is doing. Signed-off-by: Joerg Roedel <redacted> --- arch/x86/kernel/sev-es.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 0df38b185d53..79241bc45f25 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c@@ -127,14 +127,20 @@ static __always_inline bool on_vc_stack(unsigned long sp) } /* - * This function handles the case when an NMI is raised in the #VC exception - * handler entry code. In this case, the IST entry for #VC must be adjusted, so - * that any subsequent #VC exception will not overwrite the stack contents of the - * interrupted #VC handler. + * This function handles the case when an NMI is raised in the #VC + * exception handler entry code, before the #VC handler has switched off + * its IST stack. In this case, the IST entry for #VC must be adjusted, + * so that any nested #VC exception will not overwrite the stack + * contents of the interrupted #VC handler. * * The IST entry is adjusted unconditionally so that it can be also be - * unconditionally adjusted back in sev_es_ist_exit(). Otherwise a nested - * sev_es_ist_exit() call may adjust back the IST entry too early. + * unconditionally adjusted back in __sev_es_ist_exit(). Otherwise a + * nested sev_es_ist_exit() call may adjust back the IST entry too + * early. + * + * The __sev_es_ist_enter() and __sev_es_ist_exit() functions always run + * on the NMI IST stack, as they are only called from NMI handling code + * right now. */ void noinstr __sev_es_ist_enter(struct pt_regs *regs) {
@@ -143,7 +149,10 @@ void noinstr __sev_es_ist_enter(struct pt_regs *regs) /* Read old IST entry */ old_ist = __this_cpu_read(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC]); - /* Make room on the IST stack */ + /* + * Make room on the IST stack - Reserve 8 bytes to store the old + * IST entry. + */ if (on_vc_stack(regs->sp) && !user_mode(regs) && !from_syscall_gap(regs))
--
2.30.0
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