linux-kernel - Re: [PATCH v4 04/16] x86/virt/tdx: Allocate page bitmap for Dynamic PAMT

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Message-ID: <aUut+PYnX3jrSO0i@yilunxu-OptiPlex-7050>
Date: Wed, 24 Dec 2025 17:10:16 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: bp@...en8.de, chao.gao@...el.com, dave.hansen@...el.com,
	isaku.yamahata@...el.com, kai.huang@...el.com, kas@...nel.org,
	kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org, mingo@...hat.com, pbonzini@...hat.com,
	seanjc@...gle.com, tglx@...utronix.de, vannapurve@...gle.com,
	x86@...nel.org, yan.y.zhao@...el.com, xiaoyao.li@...el.com,
	binbin.wu@...el.com,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v4 04/16] x86/virt/tdx: Allocate page bitmap for Dynamic
 PAMT

> diff --git a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
> index 13ad2663488b..00ab0e550636 100644
> --- a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
> +++ b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
> @@ -33,6 +33,13 @@ static int get_tdx_sys_info_tdmr(struct tdx_sys_info_tdmr *sysinfo_tdmr)
>  		sysinfo_tdmr->pamt_2m_entry_size = val;
>  	if (!ret && !(ret = read_sys_metadata_field(0x9100000100000012, &val)))
>  		sysinfo_tdmr->pamt_1g_entry_size = val;
> +	/*
> +	 * Don't fail here if tdx_supports_dynamic_pamt() isn't supported. The
> +	 * TDX code can fallback to normal PAMT if it's not supported.
> +	 */
> +	if (!ret && tdx_supports_dynamic_pamt(&tdx_sysinfo) &&
> +	    !(ret = read_sys_metadata_field(0x9100000100000013, &val)))
> +		sysinfo_tdmr->pamt_page_bitmap_entry_bits = val;

Is it better we seal the awkward pattern inside the if (dpamt supported)  block:

	if (tdx_support_dynamic_pamt(&tdx_sysinfo))
		if (!ret && !(ret = read_sys_metadata_field(0x9100000100000013, &val)))
			sysinfo_tdmr->pamt_page_bitmap_entry_bits = val;

so we don't have to get used to another variant of the awkward pattern :)

Thanks,
Yilun

>  
>  	return ret;
>  }
> -- 
> 2.51.2
> 
>