[PATCH Part2 v5 08/45] x86/fault: Add support to handle the RMP fault for user address

@@ -19,6 +19,7 @@
 #include <linux/uaccess.h>		/* faulthandler_disabled()	*/
 #include <linux/efi.h>			/* efi_crash_gracefully_on_page_fault()*/
 #include <linux/mm_types.h>
+#include <linux/sev.h>			/* snp_lookup_rmpentry()	*/
 
 #include <asm/cpufeature.h>		/* boot_cpu_has, ...		*/
 #include <asm/traps.h>			/* dotraplinkage, ...		*/

@@ -1202,6 +1203,60 @@ do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
 }
 NOKPROBE_SYMBOL(do_kern_addr_fault);
 
+static inline size_t pages_per_hpage(int level)
+{
+	return page_level_size(level) / PAGE_SIZE;
+}
+
+/*
+ * Return 1 if the caller need to retry, 0 if it the address need to be split
+ * in order to resolve the fault.
+ */
+static int handle_user_rmp_page_fault(struct pt_regs *regs, unsigned long error_code,
+				      unsigned long address)
+{
+	int rmp_level, level;
+	pte_t *pte;
+	u64 pfn;
+
+	pte = lookup_address_in_mm(current->mm, address, &level);
+
+	/*
+	 * It can happen if there was a race between an unmap event and
+	 * the RMP fault delivery.
+	 */
+	if (!pte || !pte_present(*pte))
+		return 1;
+
+	pfn = pte_pfn(*pte);
+
+	/* If its large page then calculte the fault pfn */
+	if (level > PG_LEVEL_4K) {
+		unsigned long mask;
+
+		mask = pages_per_hpage(level) - pages_per_hpage(level - 1);
+		pfn |= (address >> PAGE_SHIFT) & mask;
+	}
+
+	/*
+	 * If its a guest private page, then the fault cannot be resolved.
+	 * Send a SIGBUS to terminate the process.
+	 */
+	if (snp_lookup_rmpentry(pfn, &rmp_level)) {
+		do_sigbus(regs, error_code, address, VM_FAULT_SIGBUS);
+		return 1;
+	}
+
+	/*
+	 * The backing page level is higher than the RMP page level, request
+	 * to split the page.
+	 */
+	if (level > rmp_level)
+		return 0;
+
+	return 1;
+}
+
 /*
  * Handle faults in the user portion of the address space.  Nothing in here
  * should check X86_PF_USER without a specific justification: for almost

@@ -1299,6 +1354,17 @@ void do_user_addr_fault(struct pt_regs *regs,
 	if (error_code & X86_PF_INSTR)
 		flags |= FAULT_FLAG_INSTRUCTION;
 
+	/*
+	 * If its an RMP violation, try resolving it.
+	 */
+	if (error_code & X86_PF_RMP) {
+		if (handle_user_rmp_page_fault(regs, error_code, address))
+			return;
+
+		/* Ask to split the page */
+		flags |= FAULT_FLAG_PAGE_SPLIT;
+	}
+
 #ifdef CONFIG_X86_64
 	/*
 	 * Faults in the vsyscall page might need emulation.  The

@@ -447,6 +447,8 @@ extern pgprot_t protection_map[16];
  * @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
  * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
  * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
+ * @FAULT_FLAG_PAGE_SPLIT: The fault was due page size mismatch, split the
+ *  region to smaller page size and retry.
  *
  * About @FAULT_FLAG_ALLOW_RETRY and @FAULT_FLAG_TRIED: we can specify
  * whether we would allow page faults to retry by specifying these two

@@ -478,6 +480,7 @@ enum fault_flag {
 	FAULT_FLAG_REMOTE =		1 << 7,
 	FAULT_FLAG_INSTRUCTION =	1 << 8,
 	FAULT_FLAG_INTERRUPTIBLE =	1 << 9,
+	FAULT_FLAG_PAGE_SPLIT =		1 << 10,
 };
 
 /*

@@ -517,7 +520,8 @@ static inline bool fault_flag_allow_retry_first(enum fault_flag flags)
 	{ FAULT_FLAG_USER,		"USER" }, \
 	{ FAULT_FLAG_REMOTE,		"REMOTE" }, \
 	{ FAULT_FLAG_INSTRUCTION,	"INSTRUCTION" }, \
-	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }
+	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }, \
+	{ FAULT_FLAG_PAGE_SPLIT,	"PAGESPLIT" }
 
 /*
  * vm_fault is filled by the pagefault handler and passed to the vma's

@@ -4589,6 +4589,15 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 	return 0;
 }
 
+static int handle_split_page_fault(struct vm_fault *vmf)
+{
+	if (!IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
+		return VM_FAULT_SIGBUS;
+
+	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
+	return 0;
+}
+
 /*
  * By the time we get here, we already hold the mm semaphore
  *

@@ -4666,6 +4675,10 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
 				pmd_migration_entry_wait(mm, vmf.pmd);
 			return 0;
 		}
+
+		if (flags & FAULT_FLAG_PAGE_SPLIT)
+			return handle_split_page_fault(&vmf);
+
 		if (pmd_trans_huge(vmf.orig_pmd) || pmd_devmap(vmf.orig_pmd)) {
 			if (pmd_protnone(vmf.orig_pmd) && vma_is_accessible(vma))
 				return do_huge_pmd_numa_page(&vmf);