Re: [PATCH] KVM: x86: Keep masked bits unmodified on kvm_set_shared_msr

[Wanpeng Li <wanpeng.li@linux.intel.com>]

Hi Nadav,
On Wed, Aug 20, 2014 at 03:11:51PM +0300, Nadav Amit wrote:
>Currently, when an msr is updated using kvm_set_shared_msr the masked bits are
>zeroed.  This behavior is currently valid since the only MSR with partial mask

Why zeroed? vmx_vcpu_setup() set all mask to -1ull.

>is EFER, in which only SCE might be unmasked. However, using the

Do you mean SCE might be masked? 

>kvm_set_shared_msr for other purposes becomes impossible.
>
>This patch keeps the masked bits unmodified while setting a shared msr.
>

Do you mean "keeps the unmasked bits unmodified" instead of "keeps the
masked bits unmodified"?

Regards,
Wanpeng Li 

>Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
>---
> arch/x86/kvm/x86.c | 1 +
> 1 file changed, 1 insertion(+)
>
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index 5f5edb6..ee42410 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -236,6 +236,7 @@ void kvm_set_shared_msr(unsigned slot, u64 value, u64 mask)
> 
> 	if (((value ^ smsr->values[slot].curr) & mask) == 0)
> 		return;
>+	value = (smsr->values[slot].curr & ~mask) | (value & mask);
> 	smsr->values[slot].curr = value;
> 	wrmsrl(shared_msrs_global.msrs[slot], value);
> 	if (!smsr->registered) {
>-- 
>1.9.1
>
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