x86/sev: Make enc_dec_hypercall() accept a size instead of npages

enc_dec_hypercall() accepted a page count instead of a size, which
forced its callers to round up. As a result, non-page aligned
vaddrs caused pages to be spuriously marked as decrypted via the
encryption status hypercall, which in turn caused consistent
corruption of pages during live migration. Live migration requires
accurate encryption status information to avoid migrating pages
from the wrong perspective.

Fixes: 064ce6c ("mm: x86: Invoke hypercall when page encryption status is changed")
Signed-off-by: Steve Rutherford <srutherford@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Tested-by: Ben Hillier <bhillier@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230824223731.2055016-1-srutherford@google.com

Author: stevenrutherford

arch/x86/include/asm/mem_encrypt.h

@@ -50,8 +50,8 @@ void __init sme_enable(struct boot_params *bp);
 
 int __init early_set_memory_decrypted(unsigned long vaddr, unsigned long size);
 int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size);
-void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages,
-					    bool enc);
+void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr,
+					    unsigned long size, bool enc);
 
 void __init mem_encrypt_free_decrypted_mem(void);
 
@@ -85,7 +85,7 @@ early_set_memory_decrypted(unsigned long vaddr, unsigned long size) { return 0;
 static inline int __init
 early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0; }
 static inline void __init
-early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages, bool enc) {}
+early_set_mem_enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool enc) {}
 
 static inline void mem_encrypt_free_decrypted_mem(void) { }
 

arch/x86/kernel/kvm.c

@@ -966,10 +966,8 @@ static void __init kvm_init_platform(void)
 		 * Ensure that _bss_decrypted section is marked as decrypted in the
 		 * shared pages list.
 		 */
-		nr_pages = DIV_ROUND_UP(__end_bss_decrypted - __start_bss_decrypted,
-					PAGE_SIZE);
 		early_set_mem_enc_dec_hypercall((unsigned long)__start_bss_decrypted,
-						nr_pages, 0);
+						__end_bss_decrypted - __start_bss_decrypted, 0);
 
 		/*
 		 * If not booted using EFI, enable Live migration support.

arch/x86/mm/mem_encrypt_amd.c

@@ -288,11 +288,10 @@ static bool amd_enc_cache_flush_required(void)
 	return !cpu_feature_enabled(X86_FEATURE_SME_COHERENT);
 }
 
-static void enc_dec_hypercall(unsigned long vaddr, int npages, bool enc)
+static void enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool enc)
 {
 #ifdef CONFIG_PARAVIRT
-	unsigned long sz = npages << PAGE_SHIFT;
-	unsigned long vaddr_end = vaddr + sz;
+	unsigned long vaddr_end = vaddr + size;
 
 	while (vaddr < vaddr_end) {
 		int psize, pmask, level;
@@ -342,7 +341,7 @@ static bool amd_enc_status_change_finish(unsigned long vaddr, int npages, bool e
 		snp_set_memory_private(vaddr, npages);
 
 	if (!cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
-		enc_dec_hypercall(vaddr, npages, enc);
+		enc_dec_hypercall(vaddr, npages << PAGE_SHIFT, enc);
 
 	return true;
 }
@@ -466,7 +465,7 @@ static int __init early_set_memory_enc_dec(unsigned long vaddr,
 
 	ret = 0;
 
-	early_set_mem_enc_dec_hypercall(start, PAGE_ALIGN(size) >> PAGE_SHIFT, enc);
+	early_set_mem_enc_dec_hypercall(start, size, enc);
 out:
 	__flush_tlb_all();
 	return ret;
@@ -482,9 +481,9 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size)
 	return early_set_memory_enc_dec(vaddr, size, true);
 }
 
-void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages, bool enc)
+void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool enc)
 {
-	enc_dec_hypercall(vaddr, npages, enc);
+	enc_dec_hypercall(vaddr, size, enc);
 }
 
 void __init sme_early_init(void)