On 4/22/2025 7:40 AM, Sean Christopherson wrote:
On Mon, Apr 21, 2025, Xin Li wrote:
It looks to me that MSR access API uses in KVM x86 are NOT consistent;
sometimes {wr,rd}msrl() are used and sometimes native_{wr,rd}msrl() are
used.
Was there a reason that how a generic or native MSR API was chosen?
I doubt anyone knows for sure; that'd likely require a time travelling device
and/or telepathic abilities :-)
In my opinion KVM should use the native MSR APIs, which can streamline
operations and potentially improve performance by avoiding the overhead
associated with generic MSR API indirect calls when CONFIG_XEN_PV=y.
As Jürgen pointed out, they aren't indirect calls. Though IIUC, there is still
Right, I didn't notice such an optimization went in.
a direct CALL and thus a RET when PARAVIRT_XXL=Y.
Correct.
I agree that using PV APIs in KVM doesn't make much sense, as running KVM in a
XEN PV guest doesn't seem like something we should optimize for, if it's even
supported. So if we end up churning all of the rdmsr/wrmsr macros, I have no
objection to switching to native variants.
Thanks for the confirmation.
Though if we do that, it would be nice if there's a way to avoid the "native_"
prefix everywhere, for the sake of readability.
Yeah, I will think about better naming them.
