diff options
| author | Sean Christopherson <seanjc@google.com> | 2025-05-22 18:17:52 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2025-06-24 13:29:31 -0700 |
| commit | c126b46e6fa87eb27e08e2120a732ec988f20eb2 (patch) | |
| tree | f11d6613bbccf57710e73fef4bef23c37080f7d8 | |
| parent | 28224ef02b56fceee2c161fe2a49a0bb197e44f5 (diff) | |
KVM: x86: Avoid calling kvm_is_mmio_pfn() when kvm_x86_ops.get_mt_mask is NULL
Guard the call to kvm_x86_call(get_mt_mask) with an explicit check on
kvm_x86_ops.get_mt_mask so as to avoid unnecessarily calling
kvm_is_mmio_pfn(), which is moderately expensive for some backing types.
E.g. lookup_memtype() conditionally takes a system-wide spinlock if KVM
ends up being call pat_pfn_immune_to_uc_mtrr(), e.g. for DAX memory.
While the call to kvm_x86_ops.get_mt_mask() itself is elided, the compiler
still needs to compute all parameters, as it can't know at build time that
the call will be squashed.
<+243>: call 0xffffffff812ad880 <kvm_is_mmio_pfn>
<+248>: mov %r13,%rsi
<+251>: mov %rbx,%rdi
<+254>: movzbl %al,%edx
<+257>: call 0xffffffff81c26af0 <__SCT__kvm_x86_get_mt_mask>
Fixes: 3fee4837ef40 ("KVM: x86: remove shadow_memtype_mask")
Tested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Link: https://lore.kernel.org/r/20250523011756.3243624-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
| -rw-r--r-- | arch/x86/kvm/mmu/spte.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c index cfce03d8f123..f262c380f40e 100644 --- a/arch/x86/kvm/mmu/spte.c +++ b/arch/x86/kvm/mmu/spte.c @@ -209,7 +209,9 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, if (level > PG_LEVEL_4K) spte |= PT_PAGE_SIZE_MASK; - spte |= kvm_x86_call(get_mt_mask)(vcpu, gfn, kvm_is_mmio_pfn(pfn)); + if (kvm_x86_ops.get_mt_mask) + spte |= kvm_x86_call(get_mt_mask)(vcpu, gfn, kvm_is_mmio_pfn(pfn)); + if (host_writable) spte |= shadow_host_writable_mask; else |