linux-kernel - [PATCH Part1 RFC v2 15/20] x86/kernel: Make the bss.decrypted section shared in RMP table

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Date:   Fri, 30 Apr 2021 07:16:11 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     tglx@...utronix.de, bp@...en8.de, jroedel@...e.de,
        thomas.lendacky@....com, pbonzini@...hat.com, mingo@...hat.com,
        dave.hansen@...el.com, rientjes@...gle.com, seanjc@...gle.com,
        peterz@...radead.org, hpa@...or.com, tony.luck@...el.com,
        Brijesh Singh <brijesh.singh@....com>
Subject: [PATCH Part1 RFC v2 15/20] x86/kernel: Make the bss.decrypted section shared in RMP table

The encryption attribute for the bss.decrypted region 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 updated in the RMP table.

Signed-off-by: Brijesh Singh <brijesh.singh@....com>
---
 arch/x86/kernel/head64.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index de01903c3735..f4c3e632345a 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -288,7 +288,14 @@ unsigned long __head __startup_64(unsigned long physaddr,
 	if (mem_encrypt_active()) {
 		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.
+			 */
+			early_snp_set_memory_shared(__pa(vaddr), __pa(vaddr), PTRS_PER_PMD);
+
 			i = pmd_index(vaddr);
 			pmd[i] -= sme_get_me_mask();
 		}
-- 
2.17.1