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Subject[PATCH] x86/intel_rdt: use rdmsr_safe() to workaround AWS host issue
It was found that AWS x1 instances (Xen-based) lack xen.git commit
1f1d183d4900 (x86/HVM: don't give the wrong impression of WRMSR succeeding)
and because of that the wrmsr_safe() check in cache_alloc_hsw_probe()
doesn't help: the consequent rdmsr() blows up with

unchecked MSR access error: RDMSR from 0xc90 at rIP:
0xffffffff88c5bba3 (native_read_msr+0x3/0x30)

The issue should definitely get fixed on AWS side. We can, however, simply
workaround this in Linux and live happily after.

Signed-off-by: Vitaly Kuznetsov <>
arch/x86/kernel/cpu/intel_rdt.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
index 44272b7107ad..0acee6cd07a8 100644
--- a/arch/x86/kernel/cpu/intel_rdt.c
+++ b/arch/x86/kernel/cpu/intel_rdt.c
@@ -213,7 +213,8 @@ static inline void cache_alloc_hsw_probe(void)

if (wrmsr_safe(IA32_L3_CBM_BASE, max_cbm, 0))
- rdmsr(IA32_L3_CBM_BASE, l, h);
+ if (rdmsr_safe(IA32_L3_CBM_BASE, &l, &h))
+ return;

/* If all the bits were set in MSR, return success */
if (l != max_cbm)
 \ /
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