[PATCH AUTOSEL 5.3 203/203] kvm: Nested KVM MMUs need PAE root too

Sasha Levin
2019-09-22T19:30:17Z

From: Jiří Paleček <jpalecek@web.de>

[ Upstream commit 1cfff4d9a5d01fa61e5768a6afffc81ae1c8ecb9 ]

On AMD processors, in PAE 32bit mode, nested KVM instances don't
work. The L0 host get a kernel OOPS, which is related to
arch.mmu->pae_root being NULL.

The reason for this is that when setting up nested KVM instance,
arch.mmu is set to &arch.guest_mmu (while normally, it would be
&arch.root_mmu). However, the initialization and allocation of
pae_root only creates it in root_mmu. KVM code (ie. in
mmu_alloc_shadow_roots) then accesses arch.mmu->pae_root, which is the
unallocated arch.guest_mmu->pae_root.

This fix just allocates (and frees) pae_root in both guest_mmu and
root_mmu (and also lm_root if it was allocated). The allocation is
subject to previous restrictions ie. it won't allocate anything on
64-bit and AFAIK not on Intel.

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=203923
Fixes: 14c07ad89f4d ("x86/kvm/mmu: introduce guest_mmu")
Signed-off-by: Jiri Palecek <jpalecek@web.de>
Tested-by: Jiri Palecek <jpalecek@web.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/mmu.c | 30 ++++++++++++++++++++++--------
1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index a63964e7cec7b..c68bf3aab12c1 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5611,13 +5611,13 @@ slot_handle_leaf(struct kvm *kvm, struct kvm_memory_slot *memslot,
PT_PAGE_TABLE_LEVEL, lock_flush_tlb);
}

-static void free_mmu_pages(struct kvm_vcpu *vcpu)
+static void free_mmu_pages(struct kvm_mmu *mmu)
{
- free_page((unsigned long)vcpu->arch.mmu->pae_root);
- free_page((unsigned long)vcpu->arch.mmu->lm_root);
+ free_page((unsigned long)mmu->pae_root);
+ free_page((unsigned long)mmu->lm_root);
}

-static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
+static int alloc_mmu_pages(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
{
struct page *page;
int i;
@@ -5638,9 +5638,9 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
if (!page)
return -ENOMEM;

- vcpu->arch.mmu->pae_root = page_address(page);
+ mmu->pae_root = page_address(page);
for (i = 0; i < 4; ++i)
- vcpu->arch.mmu->pae_root[i] = INVALID_PAGE;
+ mmu->pae_root[i] = INVALID_PAGE;

return 0;
}
@@ -5648,6 +5648,7 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
int kvm_mmu_create(struct kvm_vcpu *vcpu)
{
uint i;
+ int ret;

vcpu->arch.mmu = &vcpu->arch.root_mmu;
vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
@@ -5665,7 +5666,19 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
vcpu->arch.guest_mmu.prev_roots[i] = KVM_MMU_ROOT_INFO_INVALID;

vcpu->arch.nested_mmu.translate_gpa = translate_nested_gpa;
- return alloc_mmu_pages(vcpu);
+
+ ret = alloc_mmu_pages(vcpu, &vcpu->arch.guest_mmu);
+ if (ret)
+ return ret;
+
+ ret = alloc_mmu_pages(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;
}

@@ -6168,7 +6181,8 @@ unsigned long kvm_mmu_calculate_default_mmu_pages(struct kvm *kvm)
void kvm_mmu_destroy(struct kvm_vcpu *vcpu)
{
kvm_mmu_unload(vcpu);
- free_mmu_pages(vcpu);
+ free_mmu_pages(&vcpu->arch.root_mmu);
+ free_mmu_pages(&vcpu->arch.guest_mmu);
mmu_free_memory_caches(vcpu);
}

--
2.20.1