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Date: Tue, 4 Jun 2024 09:08:25 -0700
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Subject: Re: [PATCHv11 09/19] x86/tdx: Account shared memory
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
 Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 x86@kernel.org
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
 Peter Zijlstra <peterz@infradead.org>,
 Adrian Hunter <adrian.hunter@intel.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
 Elena Reshetova <elena.reshetova@intel.com>,
 Jun Nakajima <jun.nakajima@intel.com>,
 Rick Edgecombe <rick.p.edgecombe@intel.com>,
 Tom Lendacky <thomas.lendacky@amd.com>, "Kalra, Ashish"
 <ashish.kalra@amd.com>, Sean Christopherson <seanjc@google.com>,
 "Huang, Kai" <kai.huang@intel.com>, Ard Biesheuvel <ardb@kernel.org>,
 Baoquan He <bhe@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
 "K. Y. Srinivasan" <kys@microsoft.com>,
 Haiyang Zhang <haiyangz@microsoft.com>, kexec@lists.infradead.org,
 linux-hyperv@vger.kernel.org, linux-acpi@vger.kernel.org,
 linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org,
 Tao Liu <ltao@redhat.com>
References: <20240528095522.509667-1-kirill.shutemov@linux.intel.com>
 <20240528095522.509667-10-kirill.shutemov@linux.intel.com>
From: Dave Hansen <dave.hansen@intel.com>
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In-Reply-To: <20240528095522.509667-10-kirill.shutemov@linux.intel.com>
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On 5/28/24 02:55, Kirill A. Shutemov wrote:
> Keep track of the number of shared pages. This will allow for 
> cross-checking against the shared information in the direct mapping
> and reporting if the shared bit is lost.

It's probably also worth mentioning that conversions are slow and
relatively rare and even though a global atomic isn't really scalable,
it also isn't worth doing anything fancier.
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 26fa47db5782..979891e97d83 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -38,6 +38,8 @@
>  
>  #define TDREPORT_SUBTYPE_0	0
>  
> +static atomic_long_t nr_shared;

Doesn't this technically need to be:

	static atomic_long_t nr_shared = ATOMIC_LONG_INIT(0);

?  I thought we had some architectures where the 0 logical value wasn't
actually all 0's.