From 2f7c68cb55ecb7331f2381deb497c27155f32faf Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Wed, 03 Jan 2024 09:43:39 +0000
Subject: [PATCH] update kernel to 5.10.198
---
kernel/arch/x86/include/asm/debugreg.h | 26 ++++++++++++++++++++++++--
1 files changed, 24 insertions(+), 2 deletions(-)
diff --git a/kernel/arch/x86/include/asm/debugreg.h b/kernel/arch/x86/include/asm/debugreg.h
index cfdf307..9ed8343 100644
--- a/kernel/arch/x86/include/asm/debugreg.h
+++ b/kernel/arch/x86/include/asm/debugreg.h
@@ -39,7 +39,20 @@
asm("mov %%db6, %0" :"=r" (val));
break;
case 7:
- asm("mov %%db7, %0" :"=r" (val));
+ /*
+ * Apply __FORCE_ORDER to DR7 reads to forbid re-ordering them
+ * with other code.
+ *
+ * This is needed because a DR7 access can cause a #VC exception
+ * when running under SEV-ES. Taking a #VC exception is not a
+ * safe thing to do just anywhere in the entry code and
+ * re-ordering might place the access into an unsafe location.
+ *
+ * This happened in the NMI handler, where the DR7 read was
+ * re-ordered to happen before the call to sev_es_ist_enter(),
+ * causing stack recursion.
+ */
+ asm volatile("mov %%db7, %0" : "=r" (val) : __FORCE_ORDER);
break;
default:
BUG();
@@ -66,7 +79,16 @@
asm("mov %0, %%db6" ::"r" (value));
break;
case 7:
- asm("mov %0, %%db7" ::"r" (value));
+ /*
+ * Apply __FORCE_ORDER to DR7 writes to forbid re-ordering them
+ * with other code.
+ *
+ * While is didn't happen with a DR7 write (see the DR7 read
+ * comment above which explains where it happened), add the
+ * __FORCE_ORDER here too to avoid similar problems in the
+ * future.
+ */
+ asm volatile("mov %0, %%db7" ::"r" (value), __FORCE_ORDER);
break;
default:
BUG();
--
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