From: Joerg Roedel <jroedel@xxxxxxx>
Reorganize the code and improve the comments to make the function more
readable and easier to understand.
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
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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