x86/mm/cpa: Add sanity check for existing mappings

With the range check it is possible to do a quick verification that the
current mapping is correct vs. the static protection areas.

In case a incorrect mapping is detected a warning is emitted and the large
page is split up. If the large page is a 2M page, then the split code is
forced to check the static protections for the PTE entries to fix up the
incorrectness. For 1G pages this can't be done easily because that would
require to either find the offending 2M areas before the split or
afterwards. For now just warn about that case and revisit it when reported.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Bin Yang <bin.yang@intel.com>
Cc: Mark Gross <mark.gross@intel.com>
Link: https://lkml.kernel.org/r/20180917143546.331408643@linutronix.de

arch/x86/mm/pageattr.c

@@ -37,12 +37,14 @@ struct cpa_data {
 	unsigned long	numpages;
 	int		flags;
 	unsigned long	pfn;
-	unsigned	force_split : 1;
+	unsigned	force_split		: 1,
+			force_static_prot	: 1;
 	int		curpage;
 	struct page	**pages;
 };
 
 enum cpa_warn {
+	CPA_CONFLICT,
 	CPA_PROTECT,
 	CPA_DETECT,
 };
@@ -501,6 +503,7 @@ static inline void check_conflict(int warnlvl, pgprot_t prot, pgprotval_t val,
 				  unsigned long pfn, const char *txt)
 {
 	static const char *lvltxt[] = {
+		[CPA_CONFLICT]	= "conflict",
 		[CPA_PROTECT]	= "protect",
 		[CPA_DETECT]	= "detect",
 	};
@@ -743,7 +746,7 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
 				     struct cpa_data *cpa)
 {
 	unsigned long numpages, pmask, psize, lpaddr, addr, pfn, old_pfn;
-	pgprot_t old_prot, new_prot, req_prot;
+	pgprot_t old_prot, new_prot, req_prot, chk_prot;
 	pte_t new_pte, old_pte, *tmp;
 	enum pg_level level;
 	int i;
@@ -819,6 +822,23 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
 	lpaddr = address & pmask;
 	numpages = psize >> PAGE_SHIFT;
 
+	/*
+	 * Sanity check that the existing mapping is correct versus the static
+	 * protections. static_protections() guards against !PRESENT, so no
+	 * extra conditional required here.
+	 */
+	chk_prot = static_protections(old_prot, lpaddr, old_pfn, numpages,
+				      CPA_CONFLICT);
+
+	if (WARN_ON_ONCE(pgprot_val(chk_prot) != pgprot_val(old_prot))) {
+		/*
+		 * Split the large page and tell the split code to
+		 * enforce static protections.
+		 */
+		cpa->force_static_prot = 1;
+		return 1;
+	}
+
 	/*
 	 * Make sure that the requested pgprot does not violate the static
 	 * protections. Check the full large page whether one of the pages
@@ -828,8 +848,8 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
 	new_prot = static_protections(req_prot, address, pfn, 1, CPA_DETECT);
 	pfn = old_pfn;
 	for (i = 0, addr = lpaddr; i < numpages; i++, addr += PAGE_SIZE, pfn++) {
-		pgprot_t chk_prot = static_protections(req_prot, addr, pfn, 1,
-						       CPA_DETECT);
+		chk_prot = static_protections(req_prot, addr, pfn, 1,
+					      CPA_DETECT);
 		cpa_inc_4k_checked();
 		if (pgprot_val(chk_prot) != pgprot_val(new_prot))
 			return 1;
@@ -871,15 +891,50 @@ static int should_split_large_page(pte_t *kpte, unsigned long address,
 	return do_split;
 }
 
+static void split_set_pte(struct cpa_data *cpa, pte_t *pte, unsigned long pfn,
+			  pgprot_t ref_prot, unsigned long address,
+			  unsigned long size)
+{
+	unsigned int npg = PFN_DOWN(size);
+	pgprot_t prot;
+
+	/*
+	 * If should_split_large_page() discovered an inconsistent mapping,
+	 * remove the invalid protection in the split mapping.
+	 */
+	if (!cpa->force_static_prot)
+		goto set;
+
+	prot = static_protections(ref_prot, address, pfn, npg, CPA_PROTECT);
+
+	if (pgprot_val(prot) == pgprot_val(ref_prot))
+		goto set;
+
+	/*
+	 * If this is splitting a PMD, fix it up. PUD splits cannot be
+	 * fixed trivially as that would require to rescan the newly
+	 * installed PMD mappings after returning from split_large_page()
+	 * so an eventual further split can allocate the necessary PTE
+	 * pages. Warn for now and revisit it in case this actually
+	 * happens.
+	 */
+	if (size == PAGE_SIZE)
+		ref_prot = prot;
+	else
+		pr_warn_once("CPA: Cannot fixup static protections for PUD split\n");
+set:
+	set_pte(pte, pfn_pte(pfn, ref_prot));
+}
+
 static int
 __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 		   struct page *base)
 {
+	unsigned long lpaddr, lpinc, ref_pfn, pfn, pfninc = 1;
 	pte_t *pbase = (pte_t *)page_address(base);
-	unsigned long ref_pfn, pfn, pfninc = 1;
 	unsigned int i, level;
-	pte_t *tmp;
 	pgprot_t ref_prot;
+	pte_t *tmp;
 
 	spin_lock(&pgd_lock);
 	/*
@@ -902,15 +957,17 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 		 * PAT bit to correct position.
 		 */
 		ref_prot = pgprot_large_2_4k(ref_prot);
-
 		ref_pfn = pmd_pfn(*(pmd_t *)kpte);
+		lpaddr = address & PMD_MASK;
+		lpinc = PAGE_SIZE;
 		break;
 
 	case PG_LEVEL_1G:
 		ref_prot = pud_pgprot(*(pud_t *)kpte);
 		ref_pfn = pud_pfn(*(pud_t *)kpte);
 		pfninc = PMD_PAGE_SIZE >> PAGE_SHIFT;
-
+		lpaddr = address & PUD_MASK;
+		lpinc = PMD_SIZE;
 		/*
 		 * Clear the PSE flags if the PRESENT flag is not set
 		 * otherwise pmd_present/pmd_huge will return true
@@ -931,8 +988,8 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 	 * Get the target pfn from the original entry:
 	 */
 	pfn = ref_pfn;
-	for (i = 0; i < PTRS_PER_PTE; i++, pfn += pfninc)
-		set_pte(&pbase[i], pfn_pte(pfn, ref_prot));
+	for (i = 0; i < PTRS_PER_PTE; i++, pfn += pfninc, lpaddr += lpinc)
+		split_set_pte(cpa, pbase + i, pfn, ref_prot, lpaddr, lpinc);
 
 	if (virt_addr_valid(address)) {
 		unsigned long pfn = PFN_DOWN(__pa(address));