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Message-ID: <17930444-3740-f874-91e7-3ed81304b1a9@amd.com>
Date: Mon, 22 Apr 2024 14:46:36 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com
Cc: sathyanarayanan.kuppuswamy@...ux.intel.com, hpa@...or.com,
seanjc@...gle.com, elena.reshetova@...el.com, rick.p.edgecombe@...el.com,
x86@...nel.org, linux-kernel@...r.kernel.org, Chris Oo <cho@...rosoft.com>,
Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCHv2] x86/tdx: Preserve shared bit on mprotect()
On 4/19/24 15:13, Kirill A. Shutemov wrote:
> The TDX guest platform takes one bit from the physical address to
> indicate if the page is shared (accessible by VMM). This bit is not part
> of the physical_mask and is not preserved during mprotect(). As a
> result, the 'shared' bit is lost during mprotect() on shared mappings.
>
> _COMMON_PAGE_CHG_MASK specifies which PTE bits need to be preserved
> during modification. AMD includes 'sme_me_mask' in the define to
> preserve the 'encrypt' bit.
>
> To cover both Intel and AMD cases, include 'cc_mask' in
> _COMMON_PAGE_CHG_MASK instead of 'sme_me_mask'.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Fixes: 41394e33f3a0 ("x86/tdx: Extend the confidential computing API to support TDX guests")
> Reported-and-tested-by: Chris Oo <cho@...rosoft.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Cc: Tom Lendacky <thomas.lendacky@....com>
Appears to be no functional change on the AMD side.
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> Cc: Dexuan Cui <decui@...rosoft.com>
> ---
>
> v2:
> - Fix build for !CONFIG_ARCH_HAS_CC_PLATFORM
>
> ---
> arch/x86/include/asm/coco.h | 1 +
> arch/x86/include/asm/pgtable_types.h | 3 ++-
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/coco.h b/arch/x86/include/asm/coco.h
> index c086699b0d0c..ac8cd4447d48 100644
> --- a/arch/x86/include/asm/coco.h
> +++ b/arch/x86/include/asm/coco.h
> @@ -25,6 +25,7 @@ u64 cc_mkdec(u64 val);
> void cc_random_init(void);
> #else
> #define cc_vendor (CC_VENDOR_NONE)
> +#define cc_mask 0
>
> static inline u64 cc_mkenc(u64 val)
> {
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 8857d811fb5d..2f321137736c 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -148,7 +148,7 @@
> #define _COMMON_PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \
> _PAGE_SPECIAL | _PAGE_ACCESSED | \
> _PAGE_DIRTY_BITS | _PAGE_SOFT_DIRTY | \
> - _PAGE_DEVMAP | _PAGE_ENC | _PAGE_UFFD_WP)
> + _PAGE_DEVMAP | _PAGE_CC | _PAGE_UFFD_WP)
> #define _PAGE_CHG_MASK (_COMMON_PAGE_CHG_MASK | _PAGE_PAT)
> #define _HPAGE_CHG_MASK (_COMMON_PAGE_CHG_MASK | _PAGE_PSE | _PAGE_PAT_LARGE)
>
> @@ -173,6 +173,7 @@ enum page_cache_mode {
> };
> #endif
>
> +#define _PAGE_CC (_AT(pteval_t, cc_mask))
> #define _PAGE_ENC (_AT(pteval_t, sme_me_mask))
>
> #define _PAGE_CACHE_MASK (_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)
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