linux-kernel - Re: [PATCH v4 0/6] KVM: x86: Prep KVM hypercall handling for TDX

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Message-ID: <Z4_hsKjBS32_miZP@google.com>
Date: Tue, 21 Jan 2025 10:04:32 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tom Lendacky <thomas.lendacky@....com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	Kai Huang <kai.huang@...el.com>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH v4 0/6] KVM: x86: Prep KVM hypercall handling for TDX

On Mon, Jan 20, 2025, Binbin Wu wrote:
> On 1/18/2025 3:31 AM, Sean Christopherson wrote:
> > On Wed, Jan 15, 2025, Binbin Wu wrote:
> > > On 12/19/2024 10:40 AM, Sean Christopherson wrote:
> > > > On Wed, 27 Nov 2024 16:43:38 -0800, Sean Christopherson wrote:
> > > > > Effectively v4 of Binbin's series to handle hypercall exits to userspace in
> > > > > a generic manner, so that TDX
> > > > > 
> > > > > Binbin and Kai, this is fairly different that what we last discussed.  While
> > > > > sorting through Binbin's latest patch, I stumbled on what I think/hope is an
> > > > > approach that will make life easier for TDX.  Rather than have common code
> > > > > set the return value, _and_ have TDX implement a callback to do the same for
> > > > > user return MSRs, just use the callback for all paths.
> > > > > 
> > > > > [...]
> > > > Applied patch 1 to kvm-x86 fixes.  I'm going to hold off on the rest until the
> > > > dust settles on the SEAMCALL interfaces, e.g. in case TDX ends up marshalling
> > > > state into the "normal" GPRs.
> > > Hi Sean, Based on your suggestions in the link
> > > https://lore.kernel.org/kvm/Z1suNzg2Or743a7e@google.com, the v2 of "KVM: TDX:
> > > TDX hypercalls may exit to userspace" is planned to morph the TDG.VP.VMCALL
> > > with KVM hypercall to EXIT_REASON_VMCALL and marshall r10~r14 from
> > > vp_enter_args in struct vcpu_tdx to the appropriate x86 registers for KVM
> > > hypercall handling.
> > ...
> > 
> > > To test TDX, I made some modifications to your patch
> > > "KVM: x86: Refactor __kvm_emulate_hypercall() into a macro"
> > > Are the following changes make sense to you?
> > Yes, but I think we can go a step further and effectively revert the bulk of commit
> > e913ef159fad ("KVM: x86: Split core of hypercall emulation to helper function"),
> > i.e. have ____kvm_emulate_hypercall() read the GPRs instead of passing them in
> > via the macro.
> 
> Sure.
> 
> Are you OK if I sent the change (as a prep patch) along with v2 of
> "TDX hypercalls may exit to userspace"?

Ya, go for it.