On 09/25/2017 07:54 PM, Paolo Bonzini wrote:
On 25/09/2017 06:44, Wei Wang wrote:
+static void update_msr_autoload_count_max(void)
+{
+ u64 vmx_msr;
+ int n;
+
+ /*
+ * According to the Intel SDM, if Bits 27:25 of MSR_IA32_VMX_MISC is
+ * n, then (n + 1) * 512 is the recommended max number of MSRs to be
+ * included in the VMExit and VMEntry MSR auto switch list.
+ */
+ rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
+ n = ((vmx_msr & 0xe000000) >> 25) + 1;
+ msr_autoload_count_max = n * KVM_VMX_DEFAULT_MSR_AUTO_LOAD_COUNT;
+}
+
Any reasons to do this if it's unlikely that we'll ever update more than
512 MSRs?
Paolo
It isn't a must to allocate memory for 512 MSRs, but I think it would be
good to
allocate memory at least for 128 MSRs, because on skylake we have 32
triplets
of MSRs (FROM/TO/INFO), which are 96 in total already.
The disadvantage is that developers would need to manually calculate and
change
the number carefully when they need to add new MSRs for auto switching
in the
future. So, if consuming a little bit more memory isn't a concern, I
think we can
directly allocate memory based on what's recommended by the hardware.
Best,
Wei
