Re: [PATCH v1 1/3] KVM: x86: Convert TDP level calculation to vendor's specific code

From: Wei Huang
Date: Sun Aug 08 2021 - 15:31:10 EST




On 8/5/21 4:51 PM, Sean Christopherson wrote:

If we want to keep the MAXPHYADDR behavior, I'd vote for something like:

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b4b65c21b2ca..7e35f2bf89b4 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -97,6 +97,7 @@ module_param_named(flush_on_reuse, force_flush_and_sync_on_reuse, bool, 0644);
bool tdp_enabled = false;

static int max_huge_page_level __read_mostly;
+static int tdp_root_level __read_mostly;
static int max_tdp_level __read_mostly;

enum {
@@ -4645,6 +4646,9 @@ static union kvm_mmu_role kvm_calc_mmu_role_common(struct kvm_vcpu *vcpu,

static inline int kvm_mmu_get_tdp_level(struct kvm_vcpu *vcpu)
{
+ if (tdp_root_level)
+ return tdp_root_level;
+
/* Use 5-level TDP if and only if it's useful/necessary. */
if (max_tdp_level == 5 && cpuid_maxphyaddr(vcpu) <= 48)
return 4;
@@ -5336,10 +5340,11 @@ void kvm_mmu_invpcid_gva(struct kvm_vcpu *vcpu, gva_t gva, unsigned long pcid)
*/
}

-void kvm_configure_mmu(bool enable_tdp, int tdp_max_root_level,
- int tdp_huge_page_level)
+void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level,
+ int tdp_max_root_level, int tdp_huge_page_level)
{
tdp_enabled = enable_tdp;
+ tdp_root_level = tdp_forced_root_level;
max_tdp_level = tdp_max_root_level;

/*


I decided to take this suggestion in v2: it avoids using 5-level table (memory cost and potential table-walk overhead) if the host has the flexibility of using 4-level NPT under LA57.