linux-kernel - Re: [PATCH v19 058/130] KVM: x86/mmu: Add a private pointer to struct kvm_mmu

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Date: Mon, 22 Apr 2024 10:30:13 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Yan Zhao <yan.y.zhao@...el.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>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	Binbin Wu <binbin.wu@...ux.intel.com>,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 058/130] KVM: x86/mmu: Add a private pointer to
 struct kvm_mmu_page

On Mon, Apr 22, 2024 at 11:34:18AM +0800,
Yan Zhao <yan.y.zhao@...el.com> wrote:

> On Mon, Feb 26, 2024 at 12:26:00AM -0800, isaku.yamahata@...el.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > +static inline void *kvm_mmu_private_spt(struct kvm_mmu_page *sp)
> > +{
> > +	return sp->private_spt;
> > +}
> > +
> > +static inline void kvm_mmu_init_private_spt(struct kvm_mmu_page *sp, void *private_spt)
> > +{
> > +	sp->private_spt = private_spt;
> > +}
> This function is actually not used for initialization.
> Instead, it's only called after failure of free_private_spt() in order to
> intentionally leak the page to prevent kernel from accessing the encrypted page.
> 
> So to avoid confusion, how about renaming it to kvm_mmu_leak_private_spt() and
> always resetting the pointer to NULL?
> 
> static inline void kvm_mmu_leak_private_spt(struct kvm_mmu_page *sp)
> {
> 	sp->private_spt = NULL;
> }

The older version had a config to disable TDX TDP MMU at a compile time.  Now
we dropped the config so that we don't necessarily need wrapper function with
#ifdef. Now we have only single caller, I'll eliminate this wrapper function
(and related wrapper functions) by open code.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>