x86/mm: Refactor __set_clr_pte_enc()

Refactor __set_clr_pte_enc() and add two new helper functions to
set/clear PTE C-bit from early SEV/SNP initialization code and later
during shutdown/kexec especially when all CPUs are stopped and
interrupts are disabled and set_memory_xx() interfaces can't be used.

Co-developed-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/5df4aa450447f28294d1c5a890e27b63ed4ded36.1722520012.git.ashish.kalra@amd.com

Author: ashkalra

arch/x86/include/asm/sev.h

@@ -322,6 +322,22 @@ struct svsm_attest_call {
 	u8 rsvd[4];
 };
 
+/* PTE descriptor used for the prepare_pte_enc() operations. */
+struct pte_enc_desc {
+	pte_t *kpte;
+	int pte_level;
+	bool encrypt;
+	/* pfn of the kpte above */
+	unsigned long pfn;
+	/* physical address of @pfn */
+	unsigned long pa;
+	/* virtual address of @pfn */
+	void *va;
+	/* memory covered by the pte */
+	unsigned long size;
+	pgprot_t new_pgprot;
+};
+
 /*
  * SVSM protocol structure
  */
@@ -437,6 +453,8 @@ u64 snp_get_unsupported_features(u64 status);
 u64 sev_get_status(void);
 void sev_show_status(void);
 void snp_update_svsm_ca(void);
+int prepare_pte_enc(struct pte_enc_desc *d);
+void set_pte_enc_mask(pte_t *kpte, unsigned long pfn, pgprot_t new_prot);
 
 #else	/* !CONFIG_AMD_MEM_ENCRYPT */
 
@@ -474,6 +492,8 @@ static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
 static inline u64 sev_get_status(void) { return 0; }
 static inline void sev_show_status(void) { }
 static inline void snp_update_svsm_ca(void) { }
+static inline int prepare_pte_enc(struct pte_enc_desc *d) { return 0; }
+static inline void set_pte_enc_mask(pte_t *kpte, unsigned long pfn, pgprot_t new_prot) { }
 
 #endif	/* CONFIG_AMD_MEM_ENCRYPT */
 

arch/x86/mm/mem_encrypt_amd.c

@@ -311,59 +311,82 @@ static int amd_enc_status_change_finish(unsigned long vaddr, int npages, bool en
 	return 0;
 }
 
-static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
+int prepare_pte_enc(struct pte_enc_desc *d)
 {
-	pgprot_t old_prot, new_prot;
-	unsigned long pfn, pa, size;
-	pte_t new_pte;
+	pgprot_t old_prot;
 
-	pfn = pg_level_to_pfn(level, kpte, &old_prot);
-	if (!pfn)
-		return;
+	d->pfn = pg_level_to_pfn(d->pte_level, d->kpte, &old_prot);
+	if (!d->pfn)
+		return 1;
 
-	new_prot = old_prot;
-	if (enc)
-		pgprot_val(new_prot) |= _PAGE_ENC;
+	d->new_pgprot = old_prot;
+	if (d->encrypt)
+		pgprot_val(d->new_pgprot) |= _PAGE_ENC;
 	else
-		pgprot_val(new_prot) &= ~_PAGE_ENC;
+		pgprot_val(d->new_pgprot) &= ~_PAGE_ENC;
 
 	/* If prot is same then do nothing. */
-	if (pgprot_val(old_prot) == pgprot_val(new_prot))
-		return;
+	if (pgprot_val(old_prot) == pgprot_val(d->new_pgprot))
+		return 1;
 
-	pa = pfn << PAGE_SHIFT;
-	size = page_level_size(level);
+	d->pa = d->pfn << PAGE_SHIFT;
+	d->size = page_level_size(d->pte_level);
 
 	/*
-	 * We are going to perform in-place en-/decryption and change the
-	 * physical page attribute from C=1 to C=0 or vice versa. Flush the
-	 * caches to ensure that data gets accessed with the correct C-bit.
+	 * In-place en-/decryption and physical page attribute change
+	 * from C=1 to C=0 or vice versa will be performed. Flush the
+	 * caches to ensure that data gets accessed with the correct
+	 * C-bit.
 	 */
-	clflush_cache_range(__va(pa), size);
+	if (d->va)
+		clflush_cache_range(d->va, d->size);
+	else
+		clflush_cache_range(__va(d->pa), d->size);
+
+	return 0;
+}
+
+void set_pte_enc_mask(pte_t *kpte, unsigned long pfn, pgprot_t new_prot)
+{
+	pte_t new_pte;
+
+	/* Change the page encryption mask. */
+	new_pte = pfn_pte(pfn, new_prot);
+	set_pte_atomic(kpte, new_pte);
+}
+
+static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
+{
+	struct pte_enc_desc d = {
+		.kpte	     = kpte,
+		.pte_level   = level,
+		.encrypt     = enc
+	};
+
+	if (prepare_pte_enc(&d))
+		return;
 
 	/* Encrypt/decrypt the contents in-place */
 	if (enc) {
-		sme_early_encrypt(pa, size);
+		sme_early_encrypt(d.pa, d.size);
 	} else {
-		sme_early_decrypt(pa, size);
+		sme_early_decrypt(d.pa, d.size);
 
 		/*
 		 * ON SNP, the page state in the RMP table must happen
 		 * before the page table updates.
 		 */
-		early_snp_set_memory_shared((unsigned long)__va(pa), pa, 1);
+		early_snp_set_memory_shared((unsigned long)__va(d.pa), d.pa, 1);
 	}
 
-	/* Change the page encryption mask. */
-	new_pte = pfn_pte(pfn, new_prot);
-	set_pte_atomic(kpte, new_pte);
+	set_pte_enc_mask(kpte, d.pfn, d.new_pgprot);
 
 	/*
 	 * If page is set encrypted in the page table, then update the RMP table to
 	 * add this page as private.
 	 */
 	if (enc)
-		early_snp_set_memory_private((unsigned long)__va(pa), pa, 1);
+		early_snp_set_memory_private((unsigned long)__va(d.pa), d.pa, 1);
 }
 
 static int __init early_set_memory_enc_dec(unsigned long vaddr,