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From:   Thomas Gleixner <tglx@linutronix.de>
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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,
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        tony.luck@intel.com, vkuznets@redhat.com, wanpengli@tencent.com,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCHv2 21/29] x86/tdx: Exclude shared bit from __PHYSICAL_MASK
In-Reply-To: <20220124150215.36893-22-kirill.shutemov@linux.intel.com>
References: <20220124150215.36893-1-kirill.shutemov@linux.intel.com>
 <20220124150215.36893-22-kirill.shutemov@linux.intel.com>
Date:   Wed, 02 Feb 2022 01:18:40 +0100
Message-ID: <87ee4mw273.ffs@tglx>
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On Mon, Jan 24 2022 at 18:02, Kirill A. Shutemov wrote:

> In TDX guests, by default memory is protected from host access. If a
> guest needs to communicate with the VMM (like the I/O use case), it uses
> a single bit in the physical address to communicate the protected/shared
> attribute of the given page.
>
> In the x86 ARCH code, __PHYSICAL_MASK macro represents the width of the
> physical address in the given architecture. It is used in creating
> physical PAGE_MASK for address bits in the kernel. Since in TDX guest,
> a single bit is used as metadata, it needs to be excluded from valid
> physical address bits to avoid using incorrect addresses bits in the
> kernel.
>
> Enable DYNAMIC_PHYSICAL_MASK to support updating the __PHYSICAL_MASK.
>
> Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Impressive....

> ---
>  arch/x86/Kconfig      | 1 +
>  arch/x86/kernel/tdx.c | 8 ++++++++
>  2 files changed, 9 insertions(+)

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>