linux-kernel - Re: [RFC PATCH v2 04/23] KVM: TDX: Introduce tdx_clear

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Message-ID: <a42dae7e-4608-4488-9621-0cf32b68dfbc@linux.intel.com>
Date: Wed, 3 Sep 2025 19:19:32 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: pbonzini@...hat.com, seanjc@...gle.com, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, x86@...nel.org, rick.p.edgecombe@...el.com,
 dave.hansen@...el.com, kas@...nel.org, tabba@...gle.com,
 ackerleytng@...gle.com, quic_eberman@...cinc.com, michael.roth@....com,
 david@...hat.com, vannapurve@...gle.com, vbabka@...e.cz,
 thomas.lendacky@....com, pgonda@...gle.com, zhiquan1.li@...el.com,
 fan.du@...el.com, jun.miao@...el.com, ira.weiny@...el.com,
 isaku.yamahata@...el.com, xiaoyao.li@...el.com, chao.p.peng@...el.com
Subject: Re: [RFC PATCH v2 04/23] KVM: TDX: Introduce tdx_clear_folio() to
 clear huge pages



On 9/3/2025 5:51 PM, Yan Zhao wrote:
> On Tue, Sep 02, 2025 at 10:56:25AM +0800, Binbin Wu wrote:
>>
>> On 8/7/2025 5:42 PM, Yan Zhao wrote:
>>> After removing or reclaiming a guest private page or a control page from a
>>> TD, zero the physical page using movdir64b(), enabling the kernel to reuse
>>> the pages.
>>>
>>> Introduce the function tdx_clear_folio() to zero out physical memory using
>>> movdir64b(), starting from the page at "start_idx" within a "folio" and
>>> spanning "npages" contiguous PFNs.
>>>
>>> Convert tdx_clear_page() to be a helper function to facilitate the
>>> zeroing of 4KB pages.
>> I think this sentence is outdated?
> No? tdx_clear_page() is still invoked to clear tdr_page.

I didn't get the word "Convert".

>
>>> 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>
>>> ---
>>> RFC v2:
>>> - Add tdx_clear_folio().
>>> - Drop inner loop _tdx_clear_page() and move __mb() outside of the loop.
>>>     (Rick)
>>> - Use C99-style definition of variables inside a for loop.
>>> - Note: [1] also changes tdx_clear_page(). RFC v2 is not based on [1] now.
>>>
>>> [1] https://lore.kernel.org/all/20250724130354.79392-2-adrian.hunter@intel.com
>>>
>>> RFC v1:
>>> - split out, let tdx_clear_page() accept level.
>>> ---
>>>    arch/x86/kvm/vmx/tdx.c | 22 ++++++++++++++++------
>>>    1 file changed, 16 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
>>> index 8eaf8431c5f1..4fabefb27135 100644
>>> --- a/arch/x86/kvm/vmx/tdx.c
>>> +++ b/arch/x86/kvm/vmx/tdx.c
>>> @@ -277,18 +277,21 @@ 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_folio(struct folio *folio, unsigned long start_idx,
>>> +			    unsigned long npages)
>>>    {
>>>    	const void *zero_page = (const void *) page_to_virt(ZERO_PAGE(0));
>>> -	void *dest = page_to_virt(page);
>>> -	unsigned long i;
>>>    	/*
>>>    	 * The page could have been poisoned.  MOVDIR64B also clears
>>>    	 * the poison bit so the kernel can safely use the page again.
>>>    	 */
>>> -	for (i = 0; i < PAGE_SIZE; i += 64)
>>> -		movdir64b(dest + i, zero_page);
>>> +	for (unsigned long j = 0; j < npages; j++) {
>>> +		void *dest = page_to_virt(folio_page(folio, start_idx + j));
>>> +
>>> +		for (unsigned long i = 0; i < PAGE_SIZE; i += 64)
>>> +			movdir64b(dest + i, zero_page);
>>> +	}
>>>    	/*
>>>    	 * MOVDIR64B store uses WC buffer.  Prevent following memory reads
>>>    	 * from seeing potentially poisoned cache.
>>> @@ -296,6 +299,13 @@ static void tdx_clear_page(struct page *page)
>>>    	__mb();
>>>    }
>>> +static inline void tdx_clear_page(struct page *page)
>> No need to tag a local static function with "inline".
> Ok.
>