[PATCH v7 03/14] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]

Peter Xu
2020-03-18T16:37:54Z

Originally, we have three code paths that can dirty a page without
vcpu context for X86:

- init_rmode_identity_map
- init_rmode_tss
- kvmgt_rw_gpa

init_rmode_identity_map and init_rmode_tss will be setup on
destination VM no matter what (and the guest cannot even see them), so
it does not make sense to track them at all.

To do this, allow __x86_set_memory_region() to return the userspace
address that just allocated to the caller. Then in both of the
functions we directly write to the userspace address instead of
calling kvm_write_*() APIs.

Another trivial change is that we don't need to explicitly clear the
identity page table root in init_rmode_identity_map() because no
matter what we'll write to the whole page with 4M huge page entries.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 3 +-
arch/x86/kvm/svm.c | 9 ++--
arch/x86/kvm/vmx/vmx.c | 82 ++++++++++++++++-----------------
arch/x86/kvm/x86.c | 41 ++++++++++++++---
4 files changed, 83 insertions(+), 52 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9a183e9d4cb1..a8c68f626fb5 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1645,7 +1645,8 @@ void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu);

int kvm_is_in_guest(void);

-int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size);
+void __user *__x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
+ u32 size);
bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu);
bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu);

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 08568ae9f7a1..ae20ee4147e1 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1783,7 +1783,8 @@ static u64 *avic_get_physical_id_entry(struct kvm_vcpu *vcpu,
*/
static int avic_update_access_page(struct kvm *kvm, bool activate)
{
- int ret = 0;
+ void __user *ret;
+ int r = 0;

mutex_lock(&kvm->slots_lock);
/*
@@ -1799,13 +1800,15 @@ static int avic_update_access_page(struct kvm *kvm, bool activate)
APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
APIC_DEFAULT_PHYS_BASE,
activate ? PAGE_SIZE : 0);
- if (ret)
+ if (IS_ERR(ret)) {
+ r = PTR_ERR(ret);
goto out;
+ }

kvm->arch.apic_access_page_done = activate;
out:
mutex_unlock(&kvm->slots_lock);
- return ret;
+ return r;
}

static int avic_init_backing_page(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b447d66f44e6..a1e4fa1a61ff 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3453,34 +3453,26 @@ static bool guest_state_valid(struct kvm_vcpu *vcpu)
return true;
}

-static int init_rmode_tss(struct kvm *kvm)
+static int init_rmode_tss(struct kvm *kvm, void __user *ua)
{
- gfn_t fn;
- u16 data = 0;
- int idx, r;
+ const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
+ u16 data;
+ int i, r;
+
+ for (i = 0; i < 3; i++) {
+ r = __copy_to_user(ua + PAGE_SIZE * i, zero_page, PAGE_SIZE);
+ if (r)
+ return -EFAULT;
+ }

- idx = srcu_read_lock(&kvm->srcu);
- fn = to_kvm_vmx(kvm)->tss_addr >> PAGE_SHIFT;
- r = kvm_clear_guest_page(kvm, fn, 0, PAGE_SIZE);
- if (r < 0)
- goto out;
data = TSS_BASE_SIZE + TSS_REDIRECTION_SIZE;
- r = kvm_write_guest_page(kvm, fn++, &data,
- TSS_IOPB_BASE_OFFSET, sizeof(u16));
- if (r < 0)
- goto out;
- r = kvm_clear_guest_page(kvm, fn++, 0, PAGE_SIZE);
- if (r < 0)
- goto out;
- r = kvm_clear_guest_page(kvm, fn, 0, PAGE_SIZE);
- if (r < 0)
- goto out;
+ r = __copy_to_user(ua + TSS_IOPB_BASE_OFFSET, &data, sizeof(u16));
+ if (r)
+ return -EFAULT;
+
data = ~0;
- r = kvm_write_guest_page(kvm, fn, &data,
- RMODE_TSS_SIZE - 2 * PAGE_SIZE - 1,
- sizeof(u8));
-out:
- srcu_read_unlock(&kvm->srcu, idx);
+ r = __copy_to_user(ua + RMODE_TSS_SIZE - 1, &data, sizeof(u8));
+
return r;
}

@@ -3489,6 +3481,7 @@ static int init_rmode_identity_map(struct kvm *kvm)
struct kvm_vmx *kvm_vmx = to_kvm_vmx(kvm);
int i, r = 0;
kvm_pfn_t identity_map_pfn;
+ void __user *uaddr;
u32 tmp;

/* Protect kvm_vmx->ept_identity_pagetable_done. */
@@ -3501,22 +3494,24 @@ static int init_rmode_identity_map(struct kvm *kvm)
kvm_vmx->ept_identity_map_addr = VMX_EPT_IDENTITY_PAGETABLE_ADDR;
identity_map_pfn = kvm_vmx->ept_identity_map_addr >> PAGE_SHIFT;

- r = __x86_set_memory_region(kvm, IDENTITY_PAGETABLE_PRIVATE_MEMSLOT,
- kvm_vmx->ept_identity_map_addr, PAGE_SIZE);
- if (r < 0)
+ uaddr = __x86_set_memory_region(kvm,
+ IDENTITY_PAGETABLE_PRIVATE_MEMSLOT,
+ kvm_vmx->ept_identity_map_addr,
+ PAGE_SIZE);
+ if (IS_ERR(uaddr)) {
+ r = PTR_ERR(uaddr);
goto out;
+ }

- r = kvm_clear_guest_page(kvm, identity_map_pfn, 0, PAGE_SIZE);
- if (r < 0)
- goto out;
/* Set up identity-mapping pagetable for EPT in real mode */
for (i = 0; i < PT32_ENT_PER_PAGE; i++) {
tmp = (i << 22) + (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |
_PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_PSE);
- r = kvm_write_guest_page(kvm, identity_map_pfn,
- &tmp, i * sizeof(tmp), sizeof(tmp));
- if (r < 0)
+ r = __copy_to_user(uaddr + i * sizeof(tmp), &tmp, sizeof(tmp));
+ if (r) {
+ r = -EFAULT;
goto out;
+ }
}
kvm_vmx->ept_identity_pagetable_done = true;

@@ -3543,19 +3538,22 @@ static void seg_setup(int seg)
static int alloc_apic_access_page(struct kvm *kvm)
{
struct page *page;
- int r = 0;
+ void __user *r;
+ int ret = 0;

mutex_lock(&kvm->slots_lock);
if (kvm->arch.apic_access_page_done)
goto out;
r = __x86_set_memory_region(kvm, APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
APIC_DEFAULT_PHYS_BASE, PAGE_SIZE);
- if (r)
+ if (IS_ERR(r)) {
+ ret = PTR_ERR(r);
goto out;
+ }

page = gfn_to_page(kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
if (is_error_page(page)) {
- r = -EFAULT;
+ ret = -EFAULT;
goto out;
}

@@ -3567,7 +3565,7 @@ static int alloc_apic_access_page(struct kvm *kvm)
kvm->arch.apic_access_page_done = true;
out:
mutex_unlock(&kvm->slots_lock);
- return r;
+ return ret;
}

int allocate_vpid(void)
@@ -4494,7 +4492,7 @@ static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu)

static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr)
{
- int ret;
+ void __user *ret;

if (enable_unrestricted_guest)
return 0;
@@ -4504,10 +4502,12 @@ static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr)
PAGE_SIZE * 3);
mutex_unlock(&kvm->slots_lock);

- if (ret)
- return ret;
+ if (IS_ERR(ret))
+ return PTR_ERR(ret);
+
to_kvm_vmx(kvm)->tss_addr = addr;
- return init_rmode_tss(kvm);
+
+ return init_rmode_tss(kvm, ret);
}

static int vmx_set_identity_map_addr(struct kvm *kvm, u64 ident_addr)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e54c6ad628a8..a5123a0aa7d6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9786,7 +9786,34 @@ void kvm_arch_sync_events(struct kvm *kvm)
kvm_free_pit(kvm);
}

-int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
+#define ERR_PTR_USR(e) ((void __user *)ERR_PTR(e))
+
+/**
+ * __x86_set_memory_region: Setup KVM internal memory slot
+ *
+ * @kvm: the kvm pointer to the VM.
+ * @id: the slot ID to setup.
+ * @gpa: the GPA to install the slot (unused when @size == 0).
+ * @size: the size of the slot. Set to zero to uninstall a slot.
+ *
+ * This function helps to setup a KVM internal memory slot. Specify
+ * @size > 0 to install a new slot, while @size == 0 to uninstall a
+ * slot. The return code can be one of the following:
+ *
+ * HVA: on success (uninstall will return a bogus HVA)
+ * -errno: on error
+ *
+ * The caller should always use IS_ERR() to check the return value
+ * before use. NOTE: KVM internal memory slots are guaranteed and
+ * won't change until the VM is destroyed. This is also true to the
+ * returned HVA when installing a new memory slot. The HVA can be
+ * invalidated by either an errornous userspace program or a VM under
+ * destruction, however as long as we use __copy_{to|from}_user()
+ * properly upon the HVAs and handle the failure paths always then
+ * we're safe.
+ */
+void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
+ u32 size)
{
int i, r;
unsigned long hva, uninitialized_var(old_npages);
@@ -9795,12 +9822,12 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)

/* Called with kvm->slots_lock held. */
if (WARN_ON(id >= KVM_MEM_SLOTS_NUM))
- return -EINVAL;
+ return ERR_PTR_USR(-EINVAL);

slot = id_to_memslot(slots, id);
if (size) {
if (slot && slot->npages)
- return -EEXIST;
+ return ERR_PTR_USR(-EEXIST);

/*
* MAP_SHARED to prevent internal slot pages from being moved
@@ -9809,10 +9836,10 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
hva = vm_mmap(NULL, 0, size, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_ANONYMOUS, 0);
if (IS_ERR((void *)hva))
- return PTR_ERR((void *)hva);
+ return (void __user *)hva;
} else {
if (!slot || !slot->npages)
- return 0;
+ return ERR_PTR_USR(0);

/*
* Stuff a non-canonical value to catch use-after-delete. This
@@ -9833,13 +9860,13 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
m.memory_size = size;
r = __kvm_set_memory_region(kvm, &m);
if (r < 0)
- return r;
+ return ERR_PTR_USR(r);
}

if (!size)
vm_munmap(hva, old_npages * PAGE_SIZE);

- return 0;
+ return (void __user *)hva;
}
EXPORT_SYMBOL_GPL(__x86_set_memory_region);

--
2.24.1