[kvm-unit-tests PATCH v3 1/2] arm: Add mmu_get_pte() to the MMU API

[Nikos Nikoleris <nikos.nikoleris@xxxxxxx>]

From: Luc Maranget <Luc.Maranget@xxxxxxxx>

Add the mmu_get_pte() function that allows a test to get a pointer to
the PTE for a valid virtual address. Return NULL if the MMU is off.

Signed-off-by: Nikos Nikoleris <nikos.nikoleris@xxxxxxx>
Signed-off-by: Luc Maranget <Luc.Maranget@xxxxxxxx>
Co-Developed-by: Nikos Nikoleris <nikos.nikoleris@xxxxxxx>
Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
Reviewed-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---
 lib/arm/asm/mmu-api.h |  1 +
 lib/arm/mmu.c         | 32 +++++++++++++++++++++-----------
 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/lib/arm/asm/mmu-api.h b/lib/arm/asm/mmu-api.h
index 2bbe1fa..3d04d03 100644
--- a/lib/arm/asm/mmu-api.h
+++ b/lib/arm/asm/mmu-api.h
@@ -22,5 +22,6 @@ extern void mmu_set_range_sect(pgd_t *pgtable, uintptr_t virt_offset,
 extern void mmu_set_range_ptes(pgd_t *pgtable, uintptr_t virt_offset,
 			       phys_addr_t phys_start, phys_addr_t phys_end,
 			       pgprot_t prot);
+extern pteval_t *mmu_get_pte(pgd_t *pgtable, uintptr_t vaddr);
 extern void mmu_clear_user(pgd_t *pgtable, unsigned long vaddr);
 #endif
diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c
index d937f20..a1862a5 100644
--- a/lib/arm/mmu.c
+++ b/lib/arm/mmu.c
@@ -212,7 +212,13 @@ unsigned long __phys_to_virt(phys_addr_t addr)
 	return addr;
 }
 
-void mmu_clear_user(pgd_t *pgtable, unsigned long vaddr)
+/*
+ * NOTE: The Arm architecture might require the use of a
+ * break-before-make sequence before making changes to a PTE and
+ * certain conditions are met (see Arm ARM D5-2669 for AArch64 and
+ * B3-1378 for AArch32 for more details).
+ */
+pteval_t *mmu_get_pte(pgd_t *pgtable, uintptr_t vaddr)
 {
 	pgd_t *pgd;
 	pud_t *pud;
@@ -220,7 +226,7 @@ void mmu_clear_user(pgd_t *pgtable, unsigned long vaddr)
 	pte_t *pte;
 
 	if (!mmu_enabled())
-		return;
+		return NULL;
 
 	pgd = pgd_offset(pgtable, vaddr);
 	assert(pgd_valid(*pgd));
@@ -229,17 +235,21 @@ void mmu_clear_user(pgd_t *pgtable, unsigned long vaddr)
 	pmd = pmd_offset(pud, vaddr);
 	assert(pmd_valid(*pmd));
 
-	if (pmd_huge(*pmd)) {
-		pmd_t entry = __pmd(pmd_val(*pmd) & ~PMD_SECT_USER);
-		WRITE_ONCE(*pmd, entry);
-		goto out_flush_tlb;
-	}
+	if (pmd_huge(*pmd))
+		return &pmd_val(*pmd);
 
 	pte = pte_offset(pmd, vaddr);
 	assert(pte_valid(*pte));
-	pte_t entry = __pte(pte_val(*pte) & ~PTE_USER);
-	WRITE_ONCE(*pte, entry);
 
-out_flush_tlb:
-	flush_tlb_page(vaddr);
+        return &pte_val(*pte);
+}
+
+void mmu_clear_user(pgd_t *pgtable, unsigned long vaddr)
+{
+	pteval_t *p_pte = mmu_get_pte(pgtable, vaddr);
+	if (p_pte) {
+		pteval_t entry = *p_pte & ~PTE_USER;
+		WRITE_ONCE(*p_pte, entry);
+		flush_tlb_page(vaddr);
+	}
 }
-- 
2.17.1