[PATCH v6 28/38] KVM: arm64: Always zero invalid PTEs

[Quentin Perret]

kvm_set_invalid_pte() currently only clears bit 0 from a PTE because
stage2_map_walk_table_post() needs to be able to follow the anchor. In
preparation for re-using bits 63-01 from invalid PTEs, make sure to zero
it entirely by ensuring to cache the anchor's child upfront.

Acked-by: Will Deacon <w...@kernel.org>
Suggested-by: Will Deacon <w...@kernel.org>
Signed-off-by: Quentin Perret <qper...@google.com>
---
 arch/arm64/kvm/hyp/pgtable.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 15de1708cfcd..0a674010afb6 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -156,10 +156,9 @@ static kvm_pte_t *kvm_pte_follow(kvm_pte_t pte, struct 
kvm_pgtable_mm_ops *mm_op
        return mm_ops->phys_to_virt(kvm_pte_to_phys(pte));
 }
 
-static void kvm_set_invalid_pte(kvm_pte_t *ptep)
+static void kvm_clear_pte(kvm_pte_t *ptep)
 {
-       kvm_pte_t pte = *ptep;
-       WRITE_ONCE(*ptep, pte & ~KVM_PTE_VALID);
+       WRITE_ONCE(*ptep, 0);
 }
 
 static void kvm_set_table_pte(kvm_pte_t *ptep, kvm_pte_t *childp,
@@ -444,6 +443,7 @@ struct stage2_map_data {
        kvm_pte_t                       attr;
 
        kvm_pte_t                       *anchor;
+       kvm_pte_t                       *childp;
 
        struct kvm_s2_mmu               *mmu;
        void                            *memcache;
@@ -533,7 +533,7 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, 
u32 level,
                 * There's an existing different valid leaf entry, so perform
                 * break-before-make.
                 */
-               kvm_set_invalid_pte(ptep);
+               kvm_clear_pte(ptep);
                kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level);
                mm_ops->put_page(ptep);
        }
@@ -554,7 +554,8 @@ static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 
level,
        if (!kvm_block_mapping_supported(addr, end, data->phys, level))
                return 0;
 
-       kvm_set_invalid_pte(ptep);
+       data->childp = kvm_pte_follow(*ptep, data->mm_ops);
+       kvm_clear_pte(ptep);
 
        /*
         * Invalidate the whole stage-2, as we may have numerous leaf
@@ -600,7 +601,7 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 
level, kvm_pte_t *ptep,
         * will be mapped lazily.
         */
        if (kvm_pte_valid(pte)) {
-               kvm_set_invalid_pte(ptep);
+               kvm_clear_pte(ptep);
                kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level);
                mm_ops->put_page(ptep);
        }
@@ -616,19 +617,24 @@ static int stage2_map_walk_table_post(u64 addr, u64 end, 
u32 level,
                                      struct stage2_map_data *data)
 {
        struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
+       kvm_pte_t *childp;
        int ret = 0;
 
        if (!data->anchor)
                return 0;
 
-       mm_ops->put_page(kvm_pte_follow(*ptep, mm_ops));
-       mm_ops->put_page(ptep);
-
        if (data->anchor == ptep) {
+               childp = data->childp;
                data->anchor = NULL;
+               data->childp = NULL;
                ret = stage2_map_walk_leaf(addr, end, level, ptep, data);
+       } else {
+               childp = kvm_pte_follow(*ptep, mm_ops);
        }
 
+       mm_ops->put_page(childp);
+       mm_ops->put_page(ptep);
+
        return ret;
 }
 
@@ -737,7 +743,7 @@ static int stage2_unmap_walker(u64 addr, u64 end, u32 
level, kvm_pte_t *ptep,
         * block entry and rely on the remaining portions being faulted
         * back lazily.
         */
-       kvm_set_invalid_pte(ptep);
+       kvm_clear_pte(ptep);
        kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu, addr, level);
        mm_ops->put_page(ptep);
 
-- 
2.31.0.rc2.261.g7f71774620-goog