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KVM: arm64: Correctly handle page aging notifiers for unaligned memslot

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Userspace is allowed to select any PAGE_SIZE aligned hva to back guest
memory. This is even the case with hugepages, although it is a rather
suboptimal configuration as PTE level mappings are used at stage-2.

The arm64 page aging handlers have an assumption that the specified
range is exactly one page/block of memory, which in the aforementioned
case is not necessarily true. All together this leads to the WARN() in
kvm_age_gfn() firing.

However, the WARN is only part of the issue as the table walkers visit
at most a single leaf PTE. For hugepage-backed memory in a memslot that
isn't hugepage-aligned, page aging entirely misses accesses to the
hugepage beyond the first page in the memslot.

Add a new walker dedicated to handling page aging MMU notifiers capable
of walking a range of PTEs. Convert kvm(_test)_age_gfn() over to the new
walker and drop the WARN that caught the issue in the first place. The
implementation of this walker was inspired by the test_clear_young()
implementation by Yu Zhao [*], but repurposed to address a bug in the
existing aging implementation.

Cc: stable@vger.kernel.org # v5.15
Fixes: 056aad67f8 ("kvm: arm/arm64: Rework gpa callback handlers")
Link: https://lore.kernel.org/kvmarm/20230526234435.662652-6-yuzhao@google.com/
Co-developed-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: Reiji Watanabe <reijiw@google.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
Link: https://lore.kernel.org/r/20230627235405.4069823-1-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Oliver Upton
2023-06-27 23:54:05 +00:00
parent 970dee09b2
commit df6556adf2
3 changed files with 55 additions and 36 deletions
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47
arch/arm64/kvm/hyp/pgtable.c
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@@ -1195,25 +1195,54 @@ kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr)
return pte;
}
kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr)
struct stage2_age_data {
bool mkold;
bool young;
};
static int stage2_age_walker(const struct kvm_pgtable_visit_ctx *ctx,
enum kvm_pgtable_walk_flags visit)
{
kvm_pte_t pte = 0;
stage2_update_leaf_attrs(pgt, addr, 1, 0, KVM_PTE_LEAF_ATTR_LO_S2_AF,
&pte, NULL, 0);
kvm_pte_t new = ctx->old & ~KVM_PTE_LEAF_ATTR_LO_S2_AF;
struct stage2_age_data *data = ctx->arg;
if (!kvm_pte_valid(ctx->old) || new == ctx->old)
return 0;
data->young = true;
/*
* stage2_age_walker() is always called while holding the MMU lock for
* write, so this will always succeed. Nonetheless, this deliberately
* follows the race detection pattern of the other stage-2 walkers in
* case the locking mechanics of the MMU notifiers is ever changed.
*/
if (data->mkold && !stage2_try_set_pte(ctx, new))
return -EAGAIN;
/*
* "But where's the TLBI?!", you scream.
* "Over in the core code", I sigh.
*
* See the '->clear_flush_young()' callback on the KVM mmu notifier.
*/
return pte;
return 0;
}
bool kvm_pgtable_stage2_is_young(struct kvm_pgtable *pgt, u64 addr)
bool kvm_pgtable_stage2_test_clear_young(struct kvm_pgtable *pgt, u64 addr,
u64 size, bool mkold)
{
kvm_pte_t pte = 0;
stage2_update_leaf_attrs(pgt, addr, 1, 0, 0, &pte, NULL, 0);
return pte & KVM_PTE_LEAF_ATTR_LO_S2_AF;
struct stage2_age_data data = {
.mkold = mkold,
};
struct kvm_pgtable_walker walker = {
.cb = stage2_age_walker,
.arg = &data,
.flags = KVM_PGTABLE_WALK_LEAF,
};
WARN_ON(kvm_pgtable_walk(pgt, addr, size, &walker));
return data.young;
}
int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,