[PATCH v9 17/43] x86/kernel: Make the .bss..decrypted section shared in RMP table

[Brijesh Singh]

The encryption attribute for the .bss..decrypted section is cleared in the
initial page table build. This is because the section contains the data
that need to be shared between the guest and the hypervisor.

When SEV-SNP is active, just clearing the encryption attribute in the
page table is not enough. The page state need to be updated in the RMP
table.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/kernel/head64.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 8075e91cff2b..1239bc104cda 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -143,7 +143,21 @@ static unsigned long sme_postprocess_startup(struct boot_params *bp, pmdval_t *p
 	if (sme_get_me_mask()) {
 		vaddr = (unsigned long)__start_bss_decrypted;
 		vaddr_end = (unsigned long)__end_bss_decrypted;
+
 		for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
+			/*
+			 * When SEV-SNP is active then transition the page to
+			 * shared in the RMP table so that it is consistent with
+			 * the page table attribute change.
+			 *
+			 * At this point, kernel is running in identity mapped mode.
+			 * The __start_bss_decrypted is a regular kernel address. The
+			 * early_snp_set_memory_shared() requires a valid virtual
+			 * address, so use __pa() against __start_bss_decrypted to
+			 * get valid virtual address.
+			 */
+			early_snp_set_memory_shared(__pa(vaddr), __pa(vaddr), PTRS_PER_PMD);
+
 			i = pmd_index(vaddr);
 			pmd[i] -= sme_get_me_mask();
 		}
-- 
2.25.1