[PATCH v2 2/3] KVM: x86: Handle the case of 5-level shadow page table

Wei Huang
2021-08-08T19:27:34Z

When the 5-level page table CPU flag is exposed, KVM code needs to handle
this case by pointing mmu->root_hpa to a properly-constructed 5-level page
table.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/mmu/mmu.c | 48 +++++++++++++++++++++------------
2 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6d16f75cc8da..5d66a94ca428 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -447,6 +447,7 @@ struct kvm_mmu {

u64 *pae_root;
u64 *pml4_root;
+ u64 *pml5_root;

/*
* check zero bits on shadow page table entries, these
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index c11ee4531f6d..9985488c9524 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3430,7 +3430,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
* the shadow page table may be a PAE or a long mode page table.
*/
pm_mask = PT_PRESENT_MASK | shadow_me_mask;
- if (mmu->shadow_root_level == PT64_ROOT_4LEVEL) {
+ if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL) {
pm_mask |= PT_ACCESSED_MASK | PT_WRITABLE_MASK | PT_USER_MASK;

if (WARN_ON_ONCE(!mmu->pml4_root)) {
@@ -3457,10 +3457,19 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
mmu->pae_root[i] = root | pm_mask;
}

- if (mmu->shadow_root_level == PT64_ROOT_4LEVEL)
+ /*
+ * Depending on the shadow_root_level, build the root_hpa table by
+ * chaining either pml5->pml4->pae or pml4->pae.
+ */
+ mmu->root_hpa = __pa(mmu->pae_root);
+ if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL) {
+ mmu->pml4_root[0] = mmu->root_hpa | pm_mask;
mmu->root_hpa = __pa(mmu->pml4_root);
- else
- mmu->root_hpa = __pa(mmu->pae_root);
+ }
+ if (mmu->shadow_root_level == PT64_ROOT_5LEVEL) {
+ mmu->pml5_root[0] = mmu->root_hpa | pm_mask;
+ mmu->root_hpa = __pa(mmu->pml5_root);
+ }

set_root_pgd:
mmu->root_pgd = root_pgd;
@@ -3473,7 +3482,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
{
struct kvm_mmu *mmu = vcpu->arch.mmu;
- u64 *pml4_root, *pae_root;
+ u64 *pml5_root, *pml4_root, *pae_root;

/*
* When shadowing 32-bit or PAE NPT with 64-bit NPT, the PML4 and PDP
@@ -3485,21 +3494,15 @@ static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
mmu->shadow_root_level < PT64_ROOT_4LEVEL)
return 0;

- /*
- * This mess only works with 4-level paging and needs to be updated to
- * work with 5-level paging.
- */
- if (WARN_ON_ONCE(mmu->shadow_root_level != PT64_ROOT_4LEVEL))
- return -EIO;
-
- if (mmu->pae_root && mmu->pml4_root)
+ if (mmu->pae_root && mmu->pml4_root && mmu->pml5_root)
return 0;

/*
* The special roots should always be allocated in concert. Yell and
* bail if KVM ends up in a state where only one of the roots is valid.
*/
- if (WARN_ON_ONCE(!tdp_enabled || mmu->pae_root || mmu->pml4_root))
+ if (WARN_ON_ONCE(!tdp_enabled || mmu->pae_root || mmu->pml4_root ||
+ mmu->pml5_root))
return -EIO;

/*
@@ -3511,15 +3514,25 @@ static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
return -ENOMEM;

pml4_root = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
- if (!pml4_root) {
- free_page((unsigned long)pae_root);
- return -ENOMEM;
+ if (!pml4_root)
+ goto err_pml4;
+
+ if (mmu->shadow_root_level > PT64_ROOT_4LEVEL) {
+ pml5_root = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
+ if (!pml5_root)
+ goto err_pml5;
}

mmu->pae_root = pae_root;
mmu->pml4_root = pml4_root;
+ mmu->pml5_root = pml5_root;

return 0;
+err_pml5:
+ free_page((unsigned long)pml4_root);
+err_pml4:
+ free_page((unsigned long)pae_root);
+ return -ENOMEM;
}

void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
@@ -5338,6 +5351,7 @@ static void free_mmu_pages(struct kvm_mmu *mmu)
set_memory_encrypted((unsigned long)mmu->pae_root, 1);
free_page((unsigned long)mmu->pae_root);
free_page((unsigned long)mmu->pml4_root);
+ free_page((unsigned long)mmu->pml5_root);
}

static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
--
2.31.1