[PATCH 3/5] x86/sev-es: Optimize __sev_es_ist_enter() for better readability
From: Joerg Roedel <joro@8bytes.org>
Date: 2021-03-03 18:11:49
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> Reorganize the code and improve the comments to make the function more readable and easier to understand. Signed-off-by: Joerg Roedel <redacted> --- arch/x86/kernel/sev-es.c | 36 ++++++++++++++++++++++++------------ 1 file changed, 24 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 28b0144daddd..e1eeb3ef58c5 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c@@ -137,29 +137,41 @@ static __always_inline bool on_vc_stack(struct pt_regs *regs) } /* - * 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) { unsigned long old_ist, new_ist; /* Read old IST entry */ - old_ist = __this_cpu_read(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC]); + new_ist = old_ist = __this_cpu_read(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC]); - /* Make room on the IST stack */ + /* + * If NMI happened while on the #VC IST stack, set the new IST + * value below regs->sp, so that the interrupted stack frame is + * not overwritten by subsequent #VC exceptions. + */ if (on_vc_stack(regs)) - new_ist = ALIGN_DOWN(regs->sp, 8) - sizeof(old_ist); - else - new_ist = old_ist - sizeof(old_ist); + new_ist = regs->sp; - /* Store old IST entry */ + /* + * Reserve additional 8 bytes and store old IST value so this + * adjustment can be unrolled in __sev_es_ist_exit(). + */ + new_ist -= sizeof(old_ist); *(unsigned long *)new_ist = old_ist; /* Set new IST entry */
--
2.30.1
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