On 22.04.25 16:40, 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 a direct CALL and thus a RET when PARAVIRT_XXL=Y. 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.
Shudder. :-D No, definitely not supported. Juergen
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