[RFC PATCH 6/7] kvm: arm64: Only write protect selected PTE

[Keqian Zhu]

This function write protects all PTEs between the ffs and fls of mask.
There may has unset bit between this range. It works well under pure
software dirty log, as software dirty log is not working during this
process.

But it will unexpectly clear dirty status of PTE when hardware dirty
log is enabled. So change it to only write protect selected PTE.

Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
---
 arch/arm64/kvm/mmu.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 18717fd12731..2f8c6770a4dc 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -589,10 +589,14 @@ static void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
 		gfn_t gfn_offset, unsigned long mask)
 {
 	phys_addr_t base_gfn = slot->base_gfn + gfn_offset;
-	phys_addr_t start = (base_gfn +  __ffs(mask)) << PAGE_SHIFT;
-	phys_addr_t end = (base_gfn + __fls(mask) + 1) << PAGE_SHIFT;
+	phys_addr_t start, end;
+	int rs, re;
 
-	stage2_wp_range(&kvm->arch.mmu, start, end);
+	bitmap_for_each_set_region(&mask, rs, re, 0, BITS_PER_LONG) {
+		start = (base_gfn + rs) << PAGE_SHIFT;
+		end = (base_gfn + re) << PAGE_SHIFT;
+		stage2_wp_range(&kvm->arch.mmu, start, end);
+	}
 }
 
 /*
-- 
2.19.1