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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        mingo@redhat.com, bp@alien8.de, dave.hansen@intel.com,
        luto@kernel.org, peterz@infradead.org
Cc:     sathyanarayanan.kuppuswamy@linux.intel.com, aarcange@redhat.com,
        ak@linux.intel.com, dan.j.williams@intel.com, david@redhat.com,
        hpa@zytor.com, jgross@suse.com, jmattson@google.com,
        joro@8bytes.org, jpoimboe@redhat.com, knsathya@kernel.org,
        pbonzini@redhat.com, sdeep@vmware.com, seanjc@google.com,
        tony.luck@intel.com, vkuznets@redhat.com, wanpengli@tencent.com,
        thomas.lendacky@amd.com, brijesh.singh@amd.com, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCHv6 05/30] x86/tdx: Exclude shared bit from __PHYSICAL_MASK
In-Reply-To: <20220316020856.24435-6-kirill.shutemov@linux.intel.com>
References: <20220316020856.24435-1-kirill.shutemov@linux.intel.com>
 <20220316020856.24435-6-kirill.shutemov@linux.intel.com>
Date:   Thu, 17 Mar 2022 01:16:00 +0100
Message-ID: <87czil303j.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Wed, Mar 16 2022 at 05:08, Kirill A. Shutemov wrote:
> @@ -82,6 +82,14 @@ void __init tdx_early_init(void)
>  
>  	cc_set_vendor(CC_VENDOR_INTEL);
>  
> +	/*
> +	 * All bits above GPA width are reserved and kernel treats shared bit
> +	 * as flag, not as part of physical address.
> +	 *
> +	 * Adjust physical mask to only cover valid GPA bits.
> +	 */
> +	physical_mask &= GENMASK_ULL(gpa_width - 2, 0);
> +

Hrm. I forgot about the second use case for gpa_width, but my comment
about ordering still stands. OTOH:

         GENMASK_ULL(gpa_width - 2, 0) == BIT_UL(gpa_width - 1) - 1

right? So you really can consolidate on the fact that cc_mask is a
single bit which is above the guests physical address space boundary.

I.e. make the code tell the story instead of adding lengthy comments
explaining the obfuscation.

Thanks,

        tglx