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Subject[PATCH v4 27/34] KVM: arm64: Always zero invalid PTEs
From
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 63-02 from invalid PTEs, make sure to zero
it entirely by ensuring to cache the anchor's child upfront.

Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@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 bdd6e3d4eeb6..f37b4179b880 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,
@@ -443,6 +442,7 @@ struct stage2_map_data {
kvm_pte_t attr;

kvm_pte_t *anchor;
+ kvm_pte_t *childp;

struct kvm_s2_mmu *mmu;
void *memcache;
@@ -532,7 +532,7 @@ 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);
}
@@ -553,7 +553,8 @@ 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
@@ -599,7 +600,7 @@ 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);
}
@@ -615,19 +616,24 @@ 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;
}

@@ -736,7 +742,7 @@ 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);

--
2.30.1.766.gb4fecdf3b7-goog
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