[RFC 16/19] KVM: x86/mmu: Factor out part of vmx_get_mt_mask which does not depend on vcpu

[Ben Gardon <bgardon@google.com>]

Factor out the parts of vmx_get_mt_mask which do not depend on the vCPU
argument. This also requires adding some error reporting to the helper
function to say whether it was possible to generate the MT mask without
a vCPU argument. This refactoring will allow the MT mask to be computed
when noncoherent DMA is not enabled on a VM.

No functional change intended.


Signed-off-by: Ben Gardon <bgardon@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 77f45c005f28..4129614262e8 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6984,9 +6984,26 @@ static int __init vmx_check_processor_compat(void)
 	return 0;
 }
 
+static bool vmx_try_get_mt_mask(struct kvm *kvm, gfn_t gfn,
+				bool is_mmio, u64 *mask)
+{
+	if (is_mmio) {
+		*mask =  MTRR_TYPE_UNCACHABLE << VMX_EPT_MT_EPTE_SHIFT;
+		return true;
+	}
+
+	if (!kvm_arch_has_noncoherent_dma(kvm)) {
+		*mask = (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT;
+		return true;
+	}
+
+	return false;
+}
+
 static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
 {
 	u8 cache;
+	u64 mask;
 
 	/* We wanted to honor guest CD/MTRR/PAT, but doing so could result in
 	 * memory aliases with conflicting memory types and sometimes MCEs.
@@ -7006,11 +7023,8 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
 	 * EPT memory type is used to emulate guest CD/MTRR.
 	 */
 
-	if (is_mmio)
-		return MTRR_TYPE_UNCACHABLE << VMX_EPT_MT_EPTE_SHIFT;
-
-	if (!kvm_arch_has_noncoherent_dma(vcpu->kvm))
-		return (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT;
+	if (vmx_try_get_mt_mask(vcpu->kvm, gfn, is_mmio, &mask))
+		return mask;
 
 	if (kvm_read_cr0(vcpu) & X86_CR0_CD) {
 		if (kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
-- 
2.34.0.rc0.344.g81b53c2807-goog