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-rw-r--r--arch/x86/mm/init.c14
1 files changed, 12 insertions, 2 deletions
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index d8cfce221275..57ba5502aecf 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -77,10 +77,20 @@ static uint8_t __pte2cachemode_tbl[8] = {
[__pte2cm_idx(_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC,
};
-/* Check that the write-protect PAT entry is set for write-protect */
+/*
+ * Check that the write-protect PAT entry is set for write-protect.
+ * To do this without making assumptions how PAT has been set up (Xen has
+ * another layout than the kernel), translate the _PAGE_CACHE_MODE_WP cache
+ * mode via the __cachemode2pte_tbl[] into protection bits (those protection
+ * bits will select a cache mode of WP or better), and then translate the
+ * protection bits back into the cache mode using __pte2cm_idx() and the
+ * __pte2cachemode_tbl[] array. This will return the really used cache mode.
+ */
bool x86_has_pat_wp(void)
{
- return __pte2cachemode_tbl[_PAGE_CACHE_MODE_WP] == _PAGE_CACHE_MODE_WP;
+ uint16_t prot = __cachemode2pte_tbl[_PAGE_CACHE_MODE_WP];
+
+ return __pte2cachemode_tbl[__pte2cm_idx(prot)] == _PAGE_CACHE_MODE_WP;
}
enum page_cache_mode pgprot2cachemode(pgprot_t pgprot)