linux-kernel - Re: [PATCH] KVM: x86: Drop "cache" from user return MSR setter that skips WRMSR

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Message-ID: <aNvT8s01Q5Cr3wAq@yzhao56-desk.sh.intel.com>
Date: Tue, 30 Sep 2025 20:58:26 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
	<pbonzini@...hat.com>, <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Xiaoyao Li <xiaoyao.li@...el.com>, Rick Edgecombe
	<rick.p.edgecombe@...el.com>
Subject: Re: [PATCH] KVM: x86: Drop "cache" from user return MSR setter that
 skips WRMSR

On Tue, Sep 30, 2025 at 08:22:41PM +0800, Yan Zhao wrote:
> On Fri, Sep 19, 2025 at 02:42:59PM -0700, Sean Christopherson wrote:
> > Rename kvm_user_return_msr_update_cache() to __kvm_set_user_return_msr()
> > and use the helper kvm_set_user_return_msr() to make it obvious that the
> > double-underscores version is doing a subset of the work of the "full"
> > setter.
> > 
> > While the function does indeed update a cache, the nomenclature becomes
> > slightly misleading when adding a getter[1], as the current value isn't
> > _just_ the cached value, it's also the value that's currently loaded in
> > hardware.
> Nit:
> 
> For TDX, "it's also the value that's currently loaded in hardware" is not true.
since tdx module invokes wrmsr()s before each exit to VMM, while KVM only
invokes __kvm_set_user_return_msr() in tdx_vcpu_put().

> > Opportunistically rename "index" to "slot" in the prototypes.  The user-
> > return APIs deliberately use "slot" to try and make it more obvious that
> > they take the slot within the array, not the index of the MSR.
> > 
> > No functional change intended.
> 
> Reviewed-by: Yan Zhao <yan.y.zhao@...el.com>
> 
> > Cc: Yan Zhao <yan.y.zhao@...el.com>
> > Cc: Xiaoyao Li <xiaoyao.li@...el.com>
> > Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>
> > Link: https://lore.kernel.org/all/aM2EvzLLmBi5-iQ5@google.com [1]
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>