linux-kernel - Re: [PATCH v10 098/108] KVM: TDX: Implement callbacks for MSR operations for TDX

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Date:   Thu, 15 Dec 2022 17:29:51 -0800
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
        Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v10 098/108] KVM: TDX: Implement callbacks for MSR
 operations for TDX

On Wed, Nov 23, 2022 at 10:25:11PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> On 10/30/2022 2:23 PM, isaku.yamahata@...el.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > 
> > Implements set_msr/get_msr/has_emulated_msr methods for TDX to handle
> > hypercall from guest TD for paravirtualized rdmsr and wrmsr.  The TDX
> > module virtualizes MSRs.  For some MSRs, it injects #VE to the guest TD
> > upon RDMSR or WRMSR.  The exact list of such MSRs are defined in the spec.
> 
> How does KVM handle the case that the userland wants to get the TD MSR list?
> 
> KVM_GET_MSR_INDEX_LIST will return the global KVM MSR list, which is
> different from the TD version.

Do you mean user space VMM (e.g. qemu) by "the userland"?
There are three classes of MSRs virtualization.
- non-configurable: TDX module directly virtualizes it. VMM can't configure.
  the value set by KVM_SET_MSR_INDEX_LIST is ignored.
- configurable: TDX module directly virtualizes it. VMM can configure at the
  VM creation time.
  the value set by KVM_SET_MSR_INDEX_LIST is used.
- #VE
  VMM handles the MSR hypercall by guest TD issues. The value set by
  KVM_SET_MSR_INDEX_LIST is used.


> > Upon #VE, the guest TD may execute hypercalls,
> > TDG.VP.VMCALL<INSTRUCTION.RDMSR> and TDG.VP.VMCALL<INSTRUCTION.WRMSR>,
> > which are defined in GHCI (Guest-Host Communication Interface) so that the
> > host VMM (e.g. KVM) can virtualizes
> can virtualize

Yes, will fix.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>