On 01/03/2018 22:39, Radim Krčmář wrote: > [Resent after removing g@xxxxxxxxxxxxxxxxxx.] > > 2018-02-26 17:13-0500, Konrad Rzeszutek Wilk: >> On Sat, Feb 24, 2018 at 01:52:26AM +0100, Paolo Bonzini wrote: >>> Use the new MSR feature framework to expose the ARCH_CAPABILITIES MSR to >>> userspace. This way, userspace can access the capabilities even if it >>> does not have the permissions to read MSRs. >> >> ... That is good but could you expand a bit of why it would want this? >> >> I am 99% sure it is due to the lovely spectre_v2 mitigation but >> could you include that in the commit message so that in say a year >> folks would know what this is? > > Userspace can currently get the MSR by creating a VCPU and reading its > MSR_IA32_ARCH_CAPABILITIES, because it is set from the hardware MSR. > > I thought that "permissions to read MSRs" talked about hardware MSRs, so > the purpose of this patch would be a better interface, but I don't see > how if we keep the auto-setting on VCPU creation. Yeah, it's mostly about a better interface and being able to do checks before creating the VCPU. The commit message was written before I noticed the auto-setting on VCPU creation, and I failed to update it. Thanks, Paolo > Is this aimed towards userspaces that want nothing else from KVM than > the MSR value? > > Thanks. >
