[PATCH v19 060/130] KVM: x86/tdp_mmu: Apply mmu notifier callback to only shared GPA

isaku.yamahata
2024-02-26T08:28:22Z

From: Isaku Yamahata <isaku.yamahata@intel.com>

The private GPAs that typically guest memfd backs aren't subject to MMU
notifier because it isn't mapped into virtual address of user process.
kvm_tdp_mmu_handle_gfn() handles the callback of the MMU notifier,
clear_flush_young(), clear_young(), test_young()() and change_pte(). Make
kvm_tdp_mmu_handle_gfn() aware of private mapping and skip private mapping.

Even with AS_UNMOVABLE set, those mmu notifier are called. For example,
ksmd triggers change_pte().

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
---
v19:
- type: test_gfn() => test_young()

v18:
- newly added

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
arch/x86/kvm/mmu/tdp_mmu.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index e7514a807134..10507920f36b 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1157,9 +1157,29 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
* into this helper allow blocking; it'd be dead, wasteful code.
*/
for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
+ gfn_t start, end;
+
+ /*
+ * This function is called on behalf of mmu_notifier of
+ * clear_flush_young(), clear_young(), test_young()(), and
+ * change_pte(). They apply to only shared GPAs.
+ */
+ WARN_ON_ONCE(range->only_private);
+ WARN_ON_ONCE(!range->only_shared);
+ if (is_private_sp(root))
+ continue;
+
+ /*
+ * For TDX shared mapping, set GFN shared bit to the range,
+ * so the handler() doesn't need to set it, to avoid duplicated
+ * code in multiple handler()s.
+ */
+ start = kvm_gfn_to_shared(kvm, range->start);
+ end = kvm_gfn_to_shared(kvm, range->end);
+
rcu_read_lock();

- tdp_root_for_each_leaf_pte(iter, root, range->start, range->end)
+ tdp_root_for_each_leaf_pte(iter, root, start, end)
ret |= handler(kvm, &iter, range);

rcu_read_unlock();
--
2.25.1