[PATCH V3 08/12] KVM: X86/MMU: Allocate mmu->pae_root for PAE paging on-demand

Lai Jiangshan
2022-05-21T13:17:37Z

From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

mmu->pae_root for non-PAE paging is allocated on-demand, but
mmu->pae_root for PAE paging is allocated early when struct kvm_mmu is
being created.

Simplify the code to allocate mmu->pae_root for PAE paging and make
it on-demand.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
---
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/mmu/mmu.c | 101 +++++++++++++-------------------
arch/x86/kvm/x86.c | 4 +-
3 files changed, 44 insertions(+), 63 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9cdc5bbd721f..fb9751dfc1a7 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1615,7 +1615,7 @@ int kvm_mmu_vendor_module_init(void);
void kvm_mmu_vendor_module_exit(void);

void kvm_mmu_destroy(struct kvm_vcpu *vcpu);
-int kvm_mmu_create(struct kvm_vcpu *vcpu);
+void kvm_mmu_create(struct kvm_vcpu *vcpu);
int kvm_mmu_init_vm(struct kvm *kvm);
void kvm_mmu_uninit_vm(struct kvm *kvm);

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 90b715eefe6a..63c2b2c6122c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -668,6 +668,41 @@ static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu)
}
}

+static int mmu_alloc_pae_root(struct kvm_vcpu *vcpu)
+{
+ struct page *page;
+
+ if (vcpu->arch.mmu->root_role.level != PT32E_ROOT_LEVEL)
+ return 0;
+ if (vcpu->arch.mmu->pae_root)
+ return 0;
+
+ /*
+ * Allocate a page to hold the four PDPTEs for PAE paging when emulating
+ * 32-bit mode. CR3 is only 32 bits even on x86_64 in this case.
+ * Therefore we need to allocate the PDP table in the first 4GB of
+ * memory, which happens to fit the DMA32 zone.
+ */
+ page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_DMA32);
+ if (!page)
+ return -ENOMEM;
+ vcpu->arch.mmu->pae_root = page_address(page);
+
+ /*
+ * CR3 is only 32 bits when PAE paging is used, thus it's impossible to
+ * get the CPU to treat the PDPTEs as encrypted. Decrypt the page so
+ * that KVM's writes and the CPU's reads get along. Note, this is
+ * only necessary when using shadow paging, as 64-bit NPT can get at
+ * the C-bit even when shadowing 32-bit NPT, and SME isn't supported
+ * by 32-bit kernels (when KVM itself uses 32-bit NPT).
+ */
+ if (!tdp_enabled)
+ set_memory_decrypted((unsigned long)vcpu->arch.mmu->pae_root, 1);
+ else
+ WARN_ON_ONCE(shadow_me_value);
+ return 0;
+}
+
static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
{
int r;
@@ -5127,6 +5162,9 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu)
r = mmu_topup_memory_caches(vcpu, !vcpu->arch.mmu->root_role.direct);
if (r)
goto out;
+ r = mmu_alloc_pae_root(vcpu);
+ if (r)
+ return r;
r = mmu_alloc_special_roots(vcpu);
if (r)
goto out;
@@ -5591,63 +5629,18 @@ static void free_mmu_pages(struct kvm_mmu *mmu)
free_page((unsigned long)mmu->pml5_root);
}

-static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
+static void __kvm_mmu_create(struct kvm_mmu *mmu)
{
- struct page *page;
int i;

mmu->root.hpa = INVALID_PAGE;
mmu->root.pgd = 0;
for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++)
mmu->prev_roots[i] = KVM_MMU_ROOT_INFO_INVALID;
-
- /* vcpu->arch.guest_mmu isn't used when !tdp_enabled. */
- if (!tdp_enabled && mmu == &vcpu->arch.guest_mmu)
- return 0;
-
- /*
- * When using PAE paging, the four PDPTEs are treated as 'root' pages,
- * while the PDP table is a per-vCPU construct that's allocated at MMU
- * creation. When emulating 32-bit mode, cr3 is only 32 bits even on
- * x86_64. Therefore we need to allocate the PDP table in the first
- * 4GB of memory, which happens to fit the DMA32 zone. TDP paging
- * generally doesn't use PAE paging and can skip allocating the PDP
- * table. The main exception, handled here, is SVM's 32-bit NPT. The
- * other exception is for shadowing L1's 32-bit or PAE NPT on 64-bit
- * KVM; that horror is handled on-demand by mmu_alloc_special_roots().
- */
- if (tdp_enabled && kvm_mmu_get_tdp_level(vcpu) > PT32E_ROOT_LEVEL)
- return 0;
-
- page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_DMA32);
- if (!page)
- return -ENOMEM;
-
- mmu->pae_root = page_address(page);
-
- /*
- * CR3 is only 32 bits when PAE paging is used, thus it's impossible to
- * get the CPU to treat the PDPTEs as encrypted. Decrypt the page so
- * that KVM's writes and the CPU's reads get along. Note, this is
- * only necessary when using shadow paging, as 64-bit NPT can get at
- * the C-bit even when shadowing 32-bit NPT, and SME isn't supported
- * by 32-bit kernels (when KVM itself uses 32-bit NPT).
- */
- if (!tdp_enabled)
- set_memory_decrypted((unsigned long)mmu->pae_root, 1);
- else
- WARN_ON_ONCE(shadow_me_value);
-
- for (i = 0; i < 4; ++i)
- mmu->pae_root[i] = INVALID_PAE_ROOT;
-
- return 0;
}

-int kvm_mmu_create(struct kvm_vcpu *vcpu)
+void kvm_mmu_create(struct kvm_vcpu *vcpu)
{
- int ret;
-
vcpu->arch.mmu_pte_list_desc_cache.kmem_cache = pte_list_desc_cache;
vcpu->arch.mmu_pte_list_desc_cache.gfp_zero = __GFP_ZERO;

@@ -5659,18 +5652,8 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
vcpu->arch.mmu = &vcpu->arch.root_mmu;
vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;

- ret = __kvm_mmu_create(vcpu, &vcpu->arch.guest_mmu);
- if (ret)
- return ret;
-
- ret = __kvm_mmu_create(vcpu, &vcpu->arch.root_mmu);
- if (ret)
- goto fail_allocate_root;
-
- return ret;
- fail_allocate_root:
- free_mmu_pages(&vcpu->arch.guest_mmu);
- return ret;
+ __kvm_mmu_create(&vcpu->arch.guest_mmu);
+ __kvm_mmu_create(&vcpu->arch.root_mmu);
}

#define BATCH_ZAP_PAGES 10
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 04812eaaf61b..064aecb188dc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11285,9 +11285,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
else
vcpu->arch.mp_state = KVM_MP_STATE_UNINITIALIZED;

- r = kvm_mmu_create(vcpu);
- if (r < 0)
- return r;
+ kvm_mmu_create(vcpu);

if (irqchip_in_kernel(vcpu->kvm)) {
r = kvm_create_lapic(vcpu, lapic_timer_advance_ns);
--
2.19.1.6.gb485710b