Drop TDX's sanity check that a mirror EPT mapping isn't zapped between
creating said mapping and doing TDH.MEM.PAGE.ADD, as the check is
simultaneously superfluous and incomplete. Per commit 2608f1057601
("KVM: x86/tdp_mmu: Add a helper function to walk down the TDP MMU"), the
justification for introducing kvm_tdp_mmu_gpa_is_mapped() was to check
that the target gfn was pre-populated, with a link that points to this
snippet:
: > One small question:
: >
: > What if the memory region passed to KVM_TDX_INIT_MEM_REGION hasn't been
pre-
: > populated? If we want to make KVM_TDX_INIT_MEM_REGION work with these
regions,
: > then we still need to do the real map. Or we can make
KVM_TDX_INIT_MEM_REGION
: > return error when it finds the region hasn't been pre-populated?
:
: Return an error. I don't love the idea of bleeding so many TDX details into
: userspace, but I'm pretty sure that ship sailed a long, long time ago.
But that justification makes little sense for the final code, as the check
on nr_premapped after TDH.MEM.PAGE.ADD will detect and return an error if
KVM attempted to zap a S-EPT entry (tdx_sept_zap_private_spte() will fail
on TDH.MEM.RANGE.BLOCK due lack of a valid S-EPT entry). And as evidenced
by the "is mapped?" code being guarded with CONFIG_KVM_PROVE_MMU=y, KVM is
NOT relying on the check for general correctness.
The sanity check is also incomplete in the sense that mmu_lock is dropped
between the check and TDH.MEM.PAGE.ADD, i.e. will only detect KVM bugs that
zap SPTEs in a very specific window (note, this also applies to the check
on nr_premapped).
Removing the sanity check will allow removing kvm_tdp_mmu_gpa_is_mapped(),
which has no business being exposed to vendor code, and more importantly
will pave the way for eliminating the "pre-map" approach entirely in favor
of doing TDH.MEM.PAGE.ADD under mmu_lock.
Reviewed-by: Ira Weiny <[email protected]>
Reviewed-by: Kai Huang <[email protected]>
Reviewed-by: Binbin Wu <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/vmx/tdx.c | 14 --------------
1 file changed, 14 deletions(-)
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 326db9b9c567..4c3014befe9f 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -3181,20 +3181,6 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t
gfn, kvm_pfn_t pfn,
if (ret < 0)
goto out;
- /*
- * The private mem cannot be zapped after kvm_tdp_map_page()
- * because all paths are covered by slots_lock and the
- * filemap invalidate lock. Check that they are indeed enough.
- */
- if (IS_ENABLED(CONFIG_KVM_PROVE_MMU)) {
- scoped_guard(read_lock, &kvm->mmu_lock) {
- if (KVM_BUG_ON(!kvm_tdp_mmu_gpa_is_mapped(vcpu, gpa),
kvm)) {
- ret = -EIO;
- goto out;
- }
- }
- }
-
ret = 0;
err = tdh_mem_page_add(&kvm_tdx->td, gpa, pfn_to_page(pfn),
src_page, &entry, &level_state);
--
2.51.1.930.gacf6e81ea2-goog
