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Subject[PATCH] x86/boot: Fix SEV boot failure from change to __PHYSICAL_MASK_SHIFT
Date
In arch/x86/boot/compressed/kaslr_64.c, CONFIG_AMD_MEM_ENCRYPT support
was initially #undef'd to support SME with minimal effort. When support
for SEV was added, the #undef remained and some minimal support for
setting the encryption bit was added for building identity mapped
pagetable entries.

Commit b83ce5ee9147 ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52")
changed __PHYSICAL_MASK_SHIFT from 46 to 52 in support of 5-level paging.
This change resulted in SEV guests failing to boot because the encryption
bit was no longer being automatically masked out. The compressed boot
path now requires sme_me_mask to be defined in order for the pagetable
functions, such as pud_present(), to properly mask out the encryption bit
(currently bit 47) when evaluating pagetable entries.

Add an sme_me_mask variable in arch/x86/boot/compressed/mem_encrypt.S,
which is set when SEV is active, delete the #undef CONFIG_AMD_MEM_ENCRYPT
from arch/x86/boot/compressed/kaslr_64.c and use sme_me_mask when building
the identify mapped pagetable entries.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/boot/compressed/kaslr_64.c | 14 ++++----------
arch/x86/boot/compressed/mem_encrypt.S | 17 ++++++++++-------
arch/x86/boot/compressed/misc.h | 2 +-
3 files changed, 15 insertions(+), 18 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr_64.c b/arch/x86/boot/compressed/kaslr_64.c
index b5e5e02..522d114 100644
--- a/arch/x86/boot/compressed/kaslr_64.c
+++ b/arch/x86/boot/compressed/kaslr_64.c
@@ -16,13 +16,6 @@
#define __pa(x) ((unsigned long)(x))
#define __va(x) ((void *)((unsigned long)(x)))

-/*
- * The pgtable.h and mm/ident_map.c includes make use of the SME related
- * information which is not used in the compressed image support. Un-define
- * the SME support to avoid any compile and link errors.
- */
-#undef CONFIG_AMD_MEM_ENCRYPT
-
/* No PAGE_TABLE_ISOLATION support needed either: */
#undef CONFIG_PAGE_TABLE_ISOLATION

@@ -85,13 +78,14 @@ static void *alloc_pgt_page(void *context)
/* Locates and clears a region for a new top level page table. */
void initialize_identity_maps(void)
{
- unsigned long sev_me_mask = get_sev_encryption_mask();
+ /* If running as an SEV guest, the encryption mask is required. */
+ set_sev_encryption_mask();

/* Init mapping_info with run-time function/buffer pointers. */
mapping_info.alloc_pgt_page = alloc_pgt_page;
mapping_info.context = &pgt_data;
- mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sev_me_mask;
- mapping_info.kernpg_flag = _KERNPG_TABLE | sev_me_mask;
+ mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask;
+ mapping_info.kernpg_flag = _KERNPG_TABLE;

/*
* It should be impossible for this not to already be true,
diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
index 54f5f66..eaa843a 100644
--- a/arch/x86/boot/compressed/mem_encrypt.S
+++ b/arch/x86/boot/compressed/mem_encrypt.S
@@ -88,9 +88,7 @@ ENTRY(get_sev_encryption_bit)
ENDPROC(get_sev_encryption_bit)

.code64
-ENTRY(get_sev_encryption_mask)
- xor %rax, %rax
-
+ENTRY(set_sev_encryption_mask)
#ifdef CONFIG_AMD_MEM_ENCRYPT
push %rbp
push %rdx
@@ -101,9 +99,7 @@ ENTRY(get_sev_encryption_mask)
testl %eax, %eax
jz .Lno_sev_mask

- xor %rdx, %rdx
- bts %rax, %rdx /* Create the encryption mask */
- mov %rdx, %rax /* ... and return it */
+ bts %rax, sme_me_mask(%rip) /* Create the encryption mask */

.Lno_sev_mask:
movq %rbp, %rsp /* Restore original stack pointer */
@@ -112,9 +108,16 @@ ENTRY(get_sev_encryption_mask)
pop %rbp
#endif

+ xor %rax, %rax
ret
-ENDPROC(get_sev_encryption_mask)
+ENDPROC(set_sev_encryption_mask)

.data
enc_bit:
.int 0xffffffff
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ .balign 8
+GLOBAL(sme_me_mask)
+ .quad 0
+#endif
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 4d369c3..9e11be4 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -114,6 +114,6 @@ static inline void console_init(void)
{ }
#endif

-unsigned long get_sev_encryption_mask(void);
+void set_sev_encryption_mask(void);

#endif
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