linux-kernel - Re: [PATCH V4 1/2] x86/tdx: Eliminate duplicate code in tdx_clear

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Message-ID: <aIEGWoM-kY_6gL8N@google.com>
Date: Wed, 23 Jul 2025 08:57:14 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, pbonzini@...hat.com, vannapurve@...gle.com, 
	Tony Luck <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org, H Peter Anvin <hpa@...or.com>, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, rick.p.edgecombe@...el.com, 
	kas@...nel.org, kai.huang@...el.com, reinette.chatre@...el.com, 
	xiaoyao.li@...el.com, tony.lindgren@...ux.intel.com, 
	binbin.wu@...ux.intel.com, isaku.yamahata@...el.com, yan.y.zhao@...el.com, 
	chao.gao@...el.com
Subject: Re: [PATCH V4 1/2] x86/tdx: Eliminate duplicate code in tdx_clear_page()

On Wed, Jul 23, 2025, 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@...nel.org>
> Reviewed-by: Binbin Wu <binbin.wu@...ux.intel.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Acked-by: Kai Huang <kai.huang@...el.com>
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---

...

> 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);

Might make sense to have this be a static inline so as to avoid two exports if
KVM ever needs/wants the inner helper, but either way is a-ok by me.

Acked-by: Sean Christopherson <seanjc@...gle.com>