[tip: x86/sev] x86/sme: Use #define USE_EARLY_PGTABLE_L5 in mem_encrypt_identity.c

[tip-bot2 for Tom Lendacky]

The following commit has been merged into the x86/sev branch of tip:

Commit-ID:     e7d445ab26db833d6640d4c9a08bee176777cc82
Gitweb:        https://git.kernel.org/tip/e7d445ab26db833d6640d4c9a08bee176777cc82
Author:        Tom Lendacky <thomas.lendacky@xxxxxxx>
AuthorDate:    Fri, 15 Oct 2021 12:24:16 -05:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 19 Oct 2021 14:07:17 +02:00

x86/sme: Use #define USE_EARLY_PGTABLE_L5 in mem_encrypt_identity.c

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 the 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.

Fixes: aad983913d77 ("x86/mm/encrypt: Simplify sme_populate_pgd() and sme_populate_pgd_large()")
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.18.x
Link: https://lkml.kernel.org/r/2cb8329655f5c753905812d951e212022a480475.1634318656.git.thomas.lendacky@xxxxxxx
---
 arch/x86/mm/mem_encrypt_identity.c |  9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index 470b202..700ce8f 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -27,6 +27,15 @@
 #undef CONFIG_PARAVIRT_XXL
 #undef CONFIG_PARAVIRT_SPINLOCKS
 
+/*
+ * This code runs before CPU feature bits are set. By default, the
+ * pgtable_l5_enabled() function uses bit X86_FEATURE_LA57 to determine if
+ * 5-level paging is active, so that won't work here. USE_EARLY_PGTABLE_L5
+ * is provided to handle this situation and, instead, use a variable that
+ * has been set by the early boot code.
+ */
+#define USE_EARLY_PGTABLE_L5
+
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/mem_encrypt.h>