linux-kernel - Re: [PATCH] x86/sme: Use #define USE_EARLY_PGTABLE_L5 in mem_encrypt

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Date:   Fri, 15 Oct 2021 23:43:38 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, stable@...r.kernel.org
Subject: Re: [PATCH] x86/sme: Use #define USE_EARLY_PGTABLE_L5 in
 mem_encrypt_identity.c

On Fri, Oct 15, 2021 at 12:24:16PM -0500, Tom Lendacky wrote:
> When runtime support for converting between 4-level and 5-level pagetables
> was added to the kernel, the SME code that built pagetables was updated
> to use the pagetable functions, e.g. p4d_offset(), etc., in order to
> simplify the code. However, the use of the pagetable functions in early
> boot code requires the use of the USE_EARLY_PGTABLE_L5 #define in order to
> ensure that proper definition of pgtable_l5_enabled() is used.
> 
> Without the #define, pgtable_l5_enabled() is #defined as
> cpu_feature_enabled(X86_FEATURE_LA57). In early boot, the CPU features
> have not yet been discovered and populated, so pgtable_l5_enabled() will
> return false even when 5-level paging is enabled. This causes the SME code
> to always build 4-level pagetables to perform the in-place encryption.
> If 5-level paging is enabled, switching to the SME pagetables results in
> a page-fault that kills the boot.
> 
> Adding the #define results in pgtable_l5_enabled() using the
> __pgtable_l5_enabled variable set in early boot and the SME code building
> pagetables for the proper paging level.
> 
> Cc: <stable@...r.kernel.org> # 4.18.x
> Fixes: aad983913d77 ("x86/mm/encrypt: Simplify sme_populate_pgd() and sme_populate_pgd_large()")
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov