[PATCH v3 2/2] x86/sev: Add SNP-specific unaccepted memory support

[Tom Lendacky <thomas.lendacky@amd.com>]

Add SNP-specific hooks to the unaccepted memory support in the boot
path (__accept_memory()) and the core kernel (accept_memory()) in order
to support booting SNP guests when unaccepted memory is present. Without
this support, SNP guests will fail to boot and/or panic() when unaccepted
memory is present in the EFI memory map.

The process of accepting memory under SNP involves invoking the hypervisor
to perform a page state change for the page to private memory and then
issuing a PVALIDATE instruction to accept the page.

Create the new header file arch/x86/boot/compressed/sev.h because adding
the function declaration to any of the existing SEV related header files
pulls in too many other header files, causing the build to fail.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/Kconfig                |  1 +
 arch/x86/boot/compressed/mem.c  |  3 +++
 arch/x86/boot/compressed/sev.c  | 10 +++++++++-
 arch/x86/boot/compressed/sev.h  | 23 +++++++++++++++++++++++
 arch/x86/include/asm/sev.h      |  3 +++
 arch/x86/kernel/sev.c           | 16 ++++++++++++++++
 arch/x86/mm/unaccepted_memory.c |  4 ++++
 7 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/boot/compressed/sev.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 34146ecc5bdd..0ad53c3533c2 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1553,6 +1553,7 @@ config AMD_MEM_ENCRYPT
 	select INSTRUCTION_DECODER
 	select ARCH_HAS_CC_PLATFORM
 	select X86_MEM_ENCRYPT
+	select UNACCEPTED_MEMORY
 	help
 	  Say yes to enable support for the encryption of system memory.
 	  This requires an AMD processor that supports Secure Memory
diff --git a/arch/x86/boot/compressed/mem.c b/arch/x86/boot/compressed/mem.c
index 48e36e640da1..3e19dc0da0d7 100644
--- a/arch/x86/boot/compressed/mem.c
+++ b/arch/x86/boot/compressed/mem.c
@@ -6,6 +6,7 @@
 #include "find.h"
 #include "math.h"
 #include "tdx.h"
+#include "sev.h"
 #include <asm/shared/tdx.h>
 
 #define PMD_SHIFT	21
@@ -39,6 +40,8 @@ static inline void __accept_memory(phys_addr_t start, phys_addr_t end)
 	/* Platform-specific memory-acceptance call goes here */
 	if (is_tdx_guest())
 		tdx_accept_memory(start, end);
+	else if (sev_snp_enabled())
+		snp_accept_memory(start, end);
 	else
 		error("Cannot accept memory: unknown platform\n");
 }
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 730c4677e9db..d4b06c862094 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -115,7 +115,7 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
 /* Include code for early handlers */
 #include "../../kernel/sev-shared.c"
 
-static inline bool sev_snp_enabled(void)
+bool sev_snp_enabled(void)
 {
 	return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
 }
@@ -161,6 +161,14 @@ void snp_set_page_shared(unsigned long paddr)
 	__page_state_change(paddr, SNP_PAGE_STATE_SHARED);
 }
 
+void snp_accept_memory(phys_addr_t start, phys_addr_t end)
+{
+	while (end > start) {
+		snp_set_page_private(start);
+		start += PAGE_SIZE;
+	}
+}
+
 static bool early_setup_ghcb(void)
 {
 	if (set_page_decrypted((unsigned long)&boot_ghcb_page))
diff --git a/arch/x86/boot/compressed/sev.h b/arch/x86/boot/compressed/sev.h
new file mode 100644
index 000000000000..fc725a981b09
--- /dev/null
+++ b/arch/x86/boot/compressed/sev.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * AMD SEV header for early boot related functions.
+ *
+ * Author: Tom Lendacky <thomas.lendacky@amd.com>
+ */
+
+#ifndef BOOT_COMPRESSED_SEV_H
+#define BOOT_COMPRESSED_SEV_H
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+
+bool sev_snp_enabled(void);
+void snp_accept_memory(phys_addr_t start, phys_addr_t end);
+
+#else
+
+static inline bool sev_snp_enabled(void) { return false; }
+static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
+
+#endif
+
+#endif
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 19514524f0f8..21db66bacefe 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -202,6 +202,7 @@ void snp_set_wakeup_secondary_cpu(void);
 bool snp_init(struct boot_params *bp);
 void snp_abort(void);
 int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err);
+void snp_accept_memory(phys_addr_t start, phys_addr_t end);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -226,6 +227,8 @@ static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *in
 {
 	return -ENOTTY;
 }
+
+static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
 #endif
 
 #endif
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 40268ce97aad..d71740f54277 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -924,6 +924,22 @@ void snp_set_memory_private(unsigned long vaddr, unsigned int npages)
 	pvalidate_pages(vaddr, npages, true);
 }
 
+void snp_accept_memory(phys_addr_t start, phys_addr_t end)
+{
+	unsigned long vaddr;
+	unsigned int npages;
+
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return;
+
+	vaddr = (unsigned long)__va(start);
+	npages = (end - start) >> PAGE_SHIFT;
+
+	set_pages_state(vaddr, npages, SNP_PAGE_STATE_PRIVATE);
+
+	pvalidate_pages(vaddr, npages, true);
+}
+
 static int snp_set_vmsa(void *va, bool vmsa)
 {
 	u64 attrs;
diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c
index 9ec2304272dc..b86ad6a8ddf5 100644
--- a/arch/x86/mm/unaccepted_memory.c
+++ b/arch/x86/mm/unaccepted_memory.c
@@ -9,6 +9,7 @@
 #include <asm/setup.h>
 #include <asm/shared/tdx.h>
 #include <asm/unaccepted_memory.h>
+#include <asm/sev.h>
 
 /* Protects unaccepted memory bitmap */
 static DEFINE_SPINLOCK(unaccepted_memory_lock);
@@ -66,6 +67,9 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
 		if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
 			tdx_accept_memory(range_start * PMD_SIZE,
 					  range_end * PMD_SIZE);
+		} else if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) {
+			snp_accept_memory(range_start * PMD_SIZE,
+					  range_end * PMD_SIZE);
 		} else {
 			panic("Cannot accept memory: unknown platform\n");
 		}
-- 
2.36.1