Re: [PATCH v1 1/4] KVM/vmx: re-write the msr auto switch feature
From: Paolo Bonzini <pbonzini@redhat.com>
Date: 2017-09-25 14:24:53
Possibly related (same subject, not in this thread)
- 2017-09-25 · Re: [PATCH v1 1/4] KVM/vmx: re-write the msr auto switch feature · Paolo Bonzini <pbonzini@redhat.com>
- 2017-09-25 · [PATCH v1 1/4] KVM/vmx: re-write the msr auto switch feature · Wei Wang <hidden>
On 25/09/2017 15:02, Wei Wang wrote:
On 09/25/2017 07:54 PM, Paolo Bonzini wrote:quoted
On 25/09/2017 06:44, Wei Wang wrote:quoted
+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? PaoloIt 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.
Sure. I was just thinking that it's unnecessary to actually use VMX_MISC; sticking to one-page allocations is nicer. Paolo _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization