[Xen-devel] [PATCH v1] x86: Restore IA32_MISC_ENABLE on wakeup

["Michał Kowalczyk" <mkow@invisiblethingslab.com>]

Code in intel.c:early_init_intel() modifies IA32_MISC_ENABLE MSR. Those
modifications must be restored after resuming from S3 (see e.g. Linux wakeup
code), otherwise bad things may happen (e.g. wakeup code may cause #GP when
trying to set IA32_EFER.NXE [1]).

This bug was noticed on a ThinkPad x230 with NX disabled in the BIOS:
Xen could correctly boot, but crashed when resuming from suspend.
Applying this patch fixed the problem.

[1] Intel SDM vol 3: "If the execute-disable capability is not
available, a write to set IA32_EFER.NXE produces a #GP exception."

Signed-off-by: Michał Kowalczyk <mkow@invisiblethingslab.com>
---
 xen/arch/x86/boot/trampoline.S  |  6 +++---
 xen/arch/x86/boot/wakeup.S      | 15 +++++++++++++++
 xen/arch/x86/cpu/intel.c        |  2 +-
 xen/include/asm-x86/processor.h |  2 +-
 4 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 7c6a2328d2..fcaa3eeaf1 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -85,7 +85,7 @@ trampoline_gdt:
         .long   trampoline_gdt + BOOT_PSEUDORM_DS + 2 - .
         .popsection
 
-GLOBAL(trampoline_misc_enable_off)
+GLOBAL(misc_enable_off)
         .quad   0
 
 GLOBAL(cpuid_ext_features)
@@ -117,8 +117,8 @@ trampoline_protmode_entry:
         mov     %eax,%cr3
 
         /* Adjust IA32_MISC_ENABLE if needed (for NX enabling below). */
-        mov     bootsym_rel(trampoline_misc_enable_off,4,%esi)
-        mov     bootsym_rel(trampoline_misc_enable_off+4,4,%edi)
+        mov     bootsym_rel(misc_enable_off,4,%esi)
+        mov     bootsym_rel(misc_enable_off+4,4,%edi)
         mov     %esi,%eax
         or      %edi,%eax
         jz      1f
diff --git a/xen/arch/x86/boot/wakeup.S b/xen/arch/x86/boot/wakeup.S
index e3cb9e033a..b5f825e983 100644
--- a/xen/arch/x86/boot/wakeup.S
+++ b/xen/arch/x86/boot/wakeup.S
@@ -138,6 +138,21 @@ wakeup_32:
         add     bootsym_rel(trampoline_xen_phys_start,4,%eax)
         mov     %eax,%cr3
 
+        /* Reapply IA32_MISC_ENABLE modifications from early_init_intel(). */
+        mov     bootsym_rel(misc_enable_off, 4, %esi)
+        mov     bootsym_rel(misc_enable_off+4, 4, %edi)
+        mov     %esi, %eax
+        or      %edi, %eax
+        jz      1f
+        mov     $MSR_IA32_MISC_ENABLE, %ecx
+        rdmsr
+        not     %esi
+        not     %edi
+        and     %esi, %eax
+        and     %edi, %edx
+        wrmsr
+1:
+
         /* Will cpuid feature change after resume? */
         /* Set up EFER (Extended Feature Enable Register). */
         mov     bootsym_rel(cpuid_ext_features,4,%edi)
diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
index 5356a6ae10..a01e519281 100644
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -269,7 +269,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 				 MSR_IA32_MISC_ENABLE_XD_DISABLE);
 	if (disable) {
 		wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable & ~disable);
-		bootsym(trampoline_misc_enable_off) |= disable;
+		bootsym(misc_enable_off) |= disable;
 	}
 
 	if (disable & MSR_IA32_MISC_ENABLE_LIMIT_CPUID)
diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index 2862321eee..b325e4b0df 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -152,7 +152,7 @@ extern void (*ctxt_switch_masking)(const struct vcpu *next);
 
 extern bool_t opt_cpu_info;
 extern u32 cpuid_ext_features;
-extern u64 trampoline_misc_enable_off;
+extern u64 misc_enable_off;
 
 /* Maximum width of physical addresses supported by the hardware. */
 extern unsigned int paddr_bits;
-- 
2.11.0


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