linux-kernel - Re: [PATCH 2/2] KVM: TDX: Do not clear poisoned pages

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Message-ID: <68938275-3f6a-46fc-9b38-2c916fdec3d6@intel.com>
Date: Wed, 18 Jun 2025 07:58:17 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Adrian Hunter <adrian.hunter@...el.com>, Tony Luck <tony.luck@...el.com>,
 pbonzini@...hat.com, seanjc@...gle.com
Cc: vannapurve@...gle.com, Borislav Petkov <bp@...en8.de>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 H Peter Anvin <hpa@...or.com>, linux-edac@...r.kernel.org,
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com,
 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 2/2] KVM: TDX: Do not clear poisoned pages

On 6/18/25 05:08, Adrian Hunter wrote:
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -282,10 +282,10 @@ static void tdx_clear_page(struct page *page)
>  	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.
> -	 */
> +	/* Machine check handler may have poisoned the page */
> +	if (PageHWPoison(page))
> +		return;

I think the old comment needs to stay in some form.

There are two kinds of poisons here: One from an integrity mismatch and
the other because the hardware decided the memory is bad. MOVDIR64B
clears the integrity one, but not the hardware one obviously.

Could we make that clear in the comment, please?