linux-kernel - Re: [RFC PATCH 07/21] KVM: TDX: Add a helper for WBINVD on huge pages with TD's keyID

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Message-ID: <aCarAoK2C2bcki66@yzhao56-desk.sh.intel.com>
Date: Fri, 16 May 2025 11:03:30 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
CC: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
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	<xiaoyao.li@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Hansen,
 Dave" <dave.hansen@...el.com>, "david@...hat.com" <david@...hat.com>,
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	<pgonda@...gle.com>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 07/21] KVM: TDX: Add a helper for WBINVD on huge
 pages with TD's keyID

On Wed, May 14, 2025 at 03:29:00AM +0800, Edgecombe, Rick P wrote:
> On Thu, 2025-04-24 at 11:05 +0800, Yan Zhao wrote:
> > From: Xiaoyao Li <xiaoyao.li@...el.com>
> > 
> > After a guest page is removed from the S-EPT, KVM calls
> > tdh_phymem_page_wbinvd_hkid() to execute WBINVD on the page using the TD's
> > keyID.
> > 
> > Add a helper function that takes level information to perform WBINVD on a
> > huge page.
> > 
> > [Yan: split patch, added a helper, rebased to use struct page]
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> > ---
> >  arch/x86/kvm/vmx/tdx.c | 24 +++++++++++++++++++-----
> >  1 file changed, 19 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 69f3140928b5..355b21fc169f 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -1586,6 +1586,23 @@ int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn,
> >  	return tdx_mem_page_record_premap_cnt(kvm, level);
> >  }
> >  
> > +static inline u64 tdx_wbinvd_page(struct kvm *kvm, u64 hkid, struct page *page, int level)
> > +{
> > +	unsigned long nr = KVM_PAGES_PER_HPAGE(level);
> > +	unsigned long idx = 0;
> > +	u64 err;
> > +
> > +	while (nr--) {
> > +		err = tdh_phymem_page_wbinvd_hkid(hkid, nth_page(page, idx++));
> > +
> > +		if (KVM_BUG_ON(err, kvm)) {
> > +			pr_tdx_error(TDH_PHYMEM_PAGE_WBINVD, err);
> > +			return err;
> > +		}
> > +	}
> > +	return err;
> > +}
> 
> Hmm, did you consider changing tdh_phymem_page_wbinvd_hkid()? It's the pattern
> of KVM wrapping the SEAMCALL helpers to do some more work that needs to be
> wrapped.
SEAMCALL TDH_PHYMEM_PAGE_WBINVD only accepts a 4KB page.
Will move the loop from KVM to the wrapper in x86 if you think it's better.


> >  static int tdx_sept_drop_private_spte(struct kvm *kvm, gfn_t gfn,
> >  				      enum pg_level level, struct page *page)
> >  {
> > @@ -1625,12 +1642,9 @@ static int tdx_sept_drop_private_spte(struct kvm *kvm, gfn_t gfn,
> >  		return -EIO;
> >  	}
> >  
> > -	err = tdh_phymem_page_wbinvd_hkid((u16)kvm_tdx->hkid, page);
> > -
> > -	if (KVM_BUG_ON(err, kvm)) {
> > -		pr_tdx_error(TDH_PHYMEM_PAGE_WBINVD, err);
> > +	err = tdx_wbinvd_page(kvm, kvm_tdx->hkid, page, level);
> > +	if (err)
> >  		return -EIO;
> > -	}
> >  
> >  	tdx_clear_page(page, level);
> >  	tdx_unpin(kvm, page);
>