Jan Beulich
2010-Sep-24 12:09 UTC
[Xen-devel] [PATCH] x86: adjust MSR_IA32_MISC_ENABLE handling
In the warning message issued on writes, the Xen-modified value should
be printed (and used to determine whether anything needs to be printed
at all), as the guest kernel will usually do a read-modify-write cycle.
A question is whether Dom0 shouldn''t be allowed control over some bits,
or whether some bits shouldn''t be fully virtualized. I''m
particularly
thinking of MSR_IA32_MISC_ENABLE_FAST_STRING, which recent Linux
kernels want to disable for CONFIG_KMEMCHECK.
While putting this together I also noticed that rdmsr_safe() failed to
initialize its output registers in the failure path, thus leading to
printing of uninitialized data in the guest WRMSR warning message.
Further, the default case value-changed check can be simplified.
Signed-off-by: Jan Beulich <jbeulich@novell.com>
--- 2010-09-20.orig/xen/arch/x86/traps.c 2010-09-20 10:14:37.000000000 +0200
+++ 2010-09-20/xen/arch/x86/traps.c 2010-09-24 13:24:39.000000000 +0200
@@ -1671,6 +1671,16 @@ unsigned long guest_to_host_gpr_switch(u
void (*pv_post_outb_hook)(unsigned int port, u8 value);
+static inline uint64_t guest_misc_enable(uint64_t val)
+{
+ val &= ~(MSR_IA32_MISC_ENABLE_PERF_AVAIL |
+ MSR_IA32_MISC_ENABLE_MONITOR_ENABLE);
+ val |= MSR_IA32_MISC_ENABLE_BTS_UNAVAIL |
+ MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL |
+ MSR_IA32_MISC_ENABLE_XTPR_DISABLE;
+ return val;
+}
+
/* Instruction fetch with error handling. */
#define insn_fetch(type, base, eip, limit) \
({ unsigned long _rc, _ptr = (base) + (eip); \
@@ -2267,6 +2277,13 @@ static int emulate_privileged_op(struct
if ( wrmsr_safe(MSR_FAM10H_MMIO_CONF_BASE, msr_content) != 0 )
goto fail;
break;
+ case MSR_IA32_MISC_ENABLE:
+ if ( rdmsr_safe(regs->ecx, val) )
+ goto invalid;
+ val = guest_misc_enable(val);
+ if ( msr_content != val )
+ goto invalid;
+ break;
case MSR_IA32_MPERF:
case MSR_IA32_APERF:
if (( boot_cpu_data.x86_vendor != X86_VENDOR_INTEL ) &&
@@ -2303,8 +2320,7 @@ static int emulate_privileged_op(struct
if ( rc )
break;
- if ( (rdmsr_safe(regs->ecx, val) != 0) ||
- (eax != (uint32_t)val) || (edx != (uint32_t)(val >> 32))
)
+ if ( (rdmsr_safe(regs->ecx, val) != 0) || (msr_content != val) )
invalid:
gdprintk(XENLOG_WARNING, "Domain attempted WRMSR %p from
"
"0x%016"PRIx64" to
0x%016"PRIx64".\n",
@@ -2375,13 +2391,9 @@ static int emulate_privileged_op(struct
case MSR_IA32_MISC_ENABLE:
if ( rdmsr_safe(regs->ecx, msr_content) )
goto fail;
+ msr_content = guest_misc_enable(msr_content);
regs->eax = (uint32_t)msr_content;
regs->edx = (uint32_t)(msr_content >> 32);
- regs->eax &= ~(MSR_IA32_MISC_ENABLE_PERF_AVAIL |
- MSR_IA32_MISC_ENABLE_MONITOR_ENABLE);
- regs->eax |= MSR_IA32_MISC_ENABLE_BTS_UNAVAIL |
- MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL |
- MSR_IA32_MISC_ENABLE_XTPR_DISABLE;
break;
case MSR_EFER:
case MSR_AMD_PATCHLEVEL:
--- 2010-09-20.orig/xen/include/asm-x86/msr.h 2010-06-28 09:38:51.000000000
+0200
+++ 2010-09-20/xen/include/asm-x86/msr.h 2010-09-24 12:22:38.000000000 +0200
@@ -41,7 +41,8 @@ static inline void wrmsrl(unsigned int m
__asm__ __volatile__( \
"1: rdmsr\n2:\n" \
".section .fixup,\"ax\"\n" \
- "3: movl %5,%2\n; jmp 2b\n" \
+ "3: xorl %0,%0\n; xorl %1,%1\n" \
+ " movl %5,%2\n; jmp 2b\n" \
".previous\n" \
".section __ex_table,\"a\"\n" \
" "__FIXUP_ALIGN"\n" \
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