Re: [PATCH V5 1/3] x86/tdx: Eliminate duplicate code in tdx_clear_page()

[Adrian Hunter <adrian.hunter@intel.com>]

On 24/07/2025 15:48, Adrian Hunter wrote:
> tdx_clear_page() and reset_tdx_pages() duplicate the TDX page clearing
> logic.  Rename reset_tdx_pages() to tdx_quirk_reset_paddr() and create
> tdx_quirk_reset_page() to call tdx_quirk_reset_paddr() and be used in
> place of tdx_clear_page().
> 
> The new name reflects that, in fact, the clearing is necessary only for
> hardware with a certain quirk.  That is dealt with in a subsequent patch
> but doing the rename here avoids additional churn.
> 
> Note reset_tdx_pages() is slightly different from tdx_clear_page() because,
> more appropriately, it uses mb() in place of __mb().  Except when extra
> debugging is enabled (kcsan at present), mb() just calls __mb().
> 
> Reviewed-by: Kirill A. Shutemov <kas@kernel.org>
> Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Acked-by: Kai Huang <kai.huang@intel.com>

Forgot to add Sean's Ack from V4

> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> ---
> 
> 
> Changes in V5:
> 
> 	None
> 
> Changes in V4:
> 
> 	Add and use tdx_quirk_reset_page() for KVM (Sean)
> 
> Changes in V3:
> 
> 	Explain "quirk" rename in commit message (Rick)
> 	Explain mb() change in commit message  (Rick)
> 	Add Rev'd-by, Ack'd-by tags
> 
> Changes in V2:
> 
> 	Rename reset_tdx_pages() to tdx_quirk_reset_paddr()
> 	Call tdx_quirk_reset_paddr() directly
> 
> 
>  arch/x86/include/asm/tdx.h  |  2 ++
>  arch/x86/kvm/vmx/tdx.c      | 25 +++----------------------
>  arch/x86/virt/vmx/tdx/tdx.c | 10 ++++++++--
>  3 files changed, 13 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 7ddef3a69866..57b46f05ff97 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -131,6 +131,8 @@ int tdx_guest_keyid_alloc(void);
>  u32 tdx_get_nr_guest_keyids(void);
>  void tdx_guest_keyid_free(unsigned int keyid);
>  
> +void tdx_quirk_reset_page(struct page *page);
> +
>  struct tdx_td {
>  	/* TD root structure: */
>  	struct page *tdr_page;
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 573d6f7d1694..ebb36229c7c8 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -283,25 +283,6 @@ static inline void tdx_disassociate_vp(struct kvm_vcpu *vcpu)
>  	vcpu->cpu = -1;
>  }
>  
> -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);
> -	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);
> -	/*
> -	 * MOVDIR64B store uses WC buffer.  Prevent following memory reads
> -	 * from seeing potentially poisoned cache.
> -	 */
> -	__mb();
> -}
> -
>  static void tdx_no_vcpus_enter_start(struct kvm *kvm)
>  {
>  	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> @@ -347,7 +328,7 @@ static int tdx_reclaim_page(struct page *page)
>  
>  	r = __tdx_reclaim_page(page);
>  	if (!r)
> -		tdx_clear_page(page);
> +		tdx_quirk_reset_page(page);
>  	return r;
>  }
>  
> @@ -596,7 +577,7 @@ 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_quirk_reset_page(kvm_tdx->td.tdr_page);
>  
>  	__free_page(kvm_tdx->td.tdr_page);
>  	kvm_tdx->td.tdr_page = NULL;
> @@ -1717,7 +1698,7 @@ 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_quirk_reset_page(page);
>  	tdx_unpin(kvm, page);
>  	return 0;
>  }
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index c7a9a087ccaf..fc8d8e444f15 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -637,7 +637,7 @@ static int tdmrs_set_up_pamt_all(struct tdmr_info_list *tdmr_list,
>   * clear these pages.  Note this function doesn't flush cache of
>   * these TDX private pages.  The caller should make sure of that.
>   */
> -static void reset_tdx_pages(unsigned long base, unsigned long size)
> +static void tdx_quirk_reset_paddr(unsigned long base, unsigned long size)
>  {
>  	const void *zero_page = (const void *)page_address(ZERO_PAGE(0));
>  	unsigned long phys, end;
> @@ -654,9 +654,15 @@ static void reset_tdx_pages(unsigned long base, unsigned long size)
>  	mb();
>  }
>  
> +void tdx_quirk_reset_page(struct page *page)
> +{
> +	tdx_quirk_reset_paddr(page_to_phys(page), PAGE_SIZE);
> +}
> +EXPORT_SYMBOL_GPL(tdx_quirk_reset_page);
> +
>  static void tdmr_reset_pamt(struct tdmr_info *tdmr)
>  {
> -	tdmr_do_pamt_func(tdmr, reset_tdx_pages);
> +	tdmr_do_pamt_func(tdmr, tdx_quirk_reset_paddr);
>  }
>  
>  static void tdmrs_reset_pamt_all(struct tdmr_info_list *tdmr_list)