linux-kernel - [PATCH 1/2] x86/pat: fix x86_has_pat

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Date:   Tue,  3 May 2022 15:22:06 +0200
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     jbeulich@...e.com, Juergen Gross <jgross@...e.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 1/2] x86/pat: fix x86_has_pat_wp()

x86_has_pat_wp() is using a wrong test, as it relies on the normal
PAT configuration used by the kernel. In case the PAT MSR has been
setup by another entity (e.g. BIOS or Xen hypervisor) it might return
false even if the PAT configuration is allowing WP mappings.

Fixes: 1f6f655e01ad ("x86/mm: Add a x86_has_pat_wp() helper")
Signed-off-by: Juergen Gross <jgross@...e.com>
---
 arch/x86/mm/init.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index d8cfce221275..71e182ebced3 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -80,7 +80,8 @@ static uint8_t __pte2cachemode_tbl[8] = {
 /* Check that the write-protect PAT entry is set for write-protect */
 bool x86_has_pat_wp(void)
 {
-	return __pte2cachemode_tbl[_PAGE_CACHE_MODE_WP] == _PAGE_CACHE_MODE_WP;
+	return __pte2cachemode_tbl[__cachemode2pte_tbl[_PAGE_CACHE_MODE_WP]] ==
+	       _PAGE_CACHE_MODE_WP;
 }
 
 enum page_cache_mode pgprot2cachemode(pgprot_t pgprot)
-- 
2.35.3