linux-kernel - Re: [RFC PATCH 05/21] KVM: TDX: Enhance tdx_clear

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6e9d7b566e7e67699b012ae84d83f36de32098a5.camel@intel.com>
Date: Tue, 13 May 2025 19:17:40 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>
CC: "Shutemov, Kirill" <kirill.shutemov@...el.com>, "quic_eberman@...cinc.com"
	<quic_eberman@...cinc.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Hansen, Dave"
	<dave.hansen@...el.com>, "david@...hat.com" <david@...hat.com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>, "tabba@...gle.com"
	<tabba@...gle.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>, "Du, Fan"
	<fan.du@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "michael.roth@....com"
	<michael.roth@....com>, "Weiny, Ira" <ira.weiny@...el.com>, "vbabka@...e.cz"
	<vbabka@...e.cz>, "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
	"ackerleytng@...gle.com" <ackerleytng@...gle.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "Peng, Chao P" <chao.p.peng@...el.com>,
	"Annapurve, Vishal" <vannapurve@...gle.com>, "jroedel@...e.de"
	<jroedel@...e.de>, "Miao, Jun" <jun.miao@...el.com>, "pgonda@...gle.com"
	<pgonda@...gle.com>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 05/21] KVM: TDX: Enhance tdx_clear_page() to support
 huge pages

On Thu, 2025-04-24 at 11:05 +0800, Yan Zhao wrote:
> From: Xiaoyao Li <xiaoyao.li@...el.com>
> 
> KVM invokes tdx_clear_page() to zero pages using movdir64b().
> Include level information to enable tdx_clear_page() to zero a huge page.
> 
> [Yan: split out, let tdx_clear_page() accept level]
> 
> 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 | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 03885cb2869b..1186085795ac 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -276,7 +276,7 @@ static inline void tdx_disassociate_vp(struct kvm_vcpu *vcpu)
>  	vcpu->cpu = -1;
>  }
>  
> -static void tdx_clear_page(struct page *page)
> +static void __tdx_clear_page(struct page *page)
>  {
>  	const void *zero_page = (const void *) page_to_virt(ZERO_PAGE(0));
>  	void *dest = page_to_virt(page);
> @@ -295,6 +295,15 @@ static void tdx_clear_page(struct page *page)
>  	__mb();
>  }
>  
> +static void tdx_clear_page(struct page *page, int level)
> +{
> +	unsigned long nr = KVM_PAGES_PER_HPAGE(level);
> +	unsigned long idx = 0;
> +
> +	while (nr--)
> +		__tdx_clear_page(nth_page(page, idx++));

You shouldn't need both idx and nr.

> +}

Since tdx_clear_page() has a __mb(), it is probably worth checking that this
generates efficient code, considering the loops within loops pattern.

> +
>  static void tdx_no_vcpus_enter_start(struct kvm *kvm)
>  {
>  	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> @@ -340,11 +349,10 @@ static int tdx_reclaim_page(struct page *page)
>  
>  	r = __tdx_reclaim_page(page);
>  	if (!r)
> -		tdx_clear_page(page);
> +		tdx_clear_page(page, PG_LEVEL_4K);
>  	return r;
>  }
>  
> -
>  /*
>   * Reclaim the TD control page(s) which are crypto-protected by TDX guest's
>   * private KeyID.  Assume the cache associated with the TDX private KeyID has
> @@ -588,7 +596,7 @@ static void tdx_reclaim_td_control_pages(struct kvm *kvm)
>  		pr_tdx_error(TDH_PHYMEM_PAGE_WBINVD, err);
>  		return;
>  	}
> -	tdx_clear_page(kvm_tdx->td.tdr_page);
> +	tdx_clear_page(kvm_tdx->td.tdr_page, PG_LEVEL_4K);

Why not the __tdx_clear_page() variant? The patch adds it, but doesn't really
use it. Just implement it all in tdx_clear_page() then.

>  
>  	__free_page(kvm_tdx->td.tdr_page);
>  	kvm_tdx->td.tdr_page = NULL;
> @@ -1621,7 +1629,8 @@ static int tdx_sept_drop_private_spte(struct kvm *kvm, gfn_t gfn,
>  		pr_tdx_error(TDH_PHYMEM_PAGE_WBINVD, err);
>  		return -EIO;
>  	}
> -	tdx_clear_page(page);
> +
> +	tdx_clear_page(page, level);
>  	tdx_unpin(kvm, page);
>  	return 0;
>  }