Messages in this thread | | | Date | Wed, 6 Jul 2016 16:18:47 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] KVM: SVM: fix trashing of MSR_TSC_AUX |
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On Wed, Jul 06, 2016 at 03:43:16PM +0200, Paolo Bonzini wrote: > I don't know what I was thinking when I wrote commit 46896c73c1a4 ("KVM: > svm: add support for RDTSCP", 2015-11-12); I missed write_rdtscp_aux which > obviously uses MSR_TSC_AUX. > > Therefore we do need to save/restore MSR_TSC_AUX in svm_vcpu_run. > > Cc: stable@vger.kernel.org > Cc: Borislav Petkov <bp@alien8.de> > Fixes: 46896c73c1a4 ("KVM: svm: add support for RDTSCP") > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Something's still missing. I have a small program which does RDTSCP in the guest:
$ taskset -c 3 ./rdtscp aux1: 0x0 aux2: 0x0 p1: 195514968442, p2: 195515255582, 287140
and the aux things which are %ecx, are 0 (should be 3 in that case).
It did work with my patch with the RDTSCP intercept:
$ taskset -c 3 ./rdtscp aux1: 0x3 aux2: 0x3 p1: 157117003683, p2: 157119280794, 2277111
Btw, just for my own understanding: if we don't intercept RDTSCP, does it get emulated? Where does the TSC value come from, qemu?
Here's the program.
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#include <stdio.h> #include <stdlib.h> #include <unistd.h>
typedef unsigned long long u64;
#define DECLARE_ARGS(val, low, high) unsigned low, high #define EAX_EDX_VAL(val, low, high) ((low) | ((u64)(high) << 32)) #define EAX_EDX_ARGS(val, low, high) "a" (low), "d" (high) #define EAX_EDX_RET(val, low, high) "=a" (low), "=d" (high)
static __always_inline unsigned long long rdtscp(unsigned int *aux) { unsigned int lo, hi;
asm volatile("rdtscp" : "=a" (lo), "=d" (hi), "=c" (*aux));
return EAX_EDX_VAL(0, lo, hi); }
int main() { unsigned long long p1, p2; unsigned int aux;
p1 = rdtscp(&aux); printf("aux1: 0x%x\n", aux); p2 = rdtscp(&aux); printf("aux2: 0x%x\n", aux);
printf("p1: %llu, p2: %llu, %lld\n", p1, p2, p2 - p1);
return 0; }
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply.
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