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From:   "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To:     tglx@linutronix.de, 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,
        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: [PATCHv4 06/30] x86/tdx: Exclude shared bit from __PHYSICAL_MASK
Date:   Thu, 24 Feb 2022 18:56:06 +0300
Message-Id: <20220224155630.52734-7-kirill.shutemov@linux.intel.com>
In-Reply-To: <20220224155630.52734-1-kirill.shutemov@linux.intel.com>
References: <20220224155630.52734-1-kirill.shutemov@linux.intel.com>
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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>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/Kconfig    | 1 +
 arch/x86/coco/tdx.c | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 93e67842e369..d2f45e58e846 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -885,6 +885,7 @@ config INTEL_TDX_GUEST
 	depends on X86_64 && CPU_SUP_INTEL
 	depends on X86_X2APIC
 	select ARCH_HAS_CC_PLATFORM
+	select DYNAMIC_PHYSICAL_MASK
 	help
 	  Support running as a guest under Intel TDX.  Without this support,
 	  the guest kernel can not boot or run under TDX.
diff --git a/arch/x86/coco/tdx.c b/arch/x86/coco/tdx.c
index 74c6e68dd1b3..14c085930b5f 100644
--- a/arch/x86/coco/tdx.c
+++ b/arch/x86/coco/tdx.c
@@ -74,6 +74,14 @@ 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(td_info.gpa_width - 2, 0);
+
 	/*
 	 * The highest bit of a guest physical address is the "sharing" bit.
 	 * Set it for shared pages and clear it for private pages.
-- 
2.34.1