[PATCH 09/10] KVM: introduce readonly memslot
From: Xiao Guangrong
Date: Tue Jul 17 2012 - 10:46:21 EST
In current code, if we map a readonly memory space from host to guest
and the page is not currently mapped in the host, we will get a fault-pfn
and async is not allowed, then the vm will crash
We introduce readonly memory region to map ROM/ROMD to the guest, read access
is happy for readonly memslot, write access on readonly memslot will cause
KVM_EXIT_MMIO exit
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
---
Documentation/virtual/kvm/api.txt | 10 +++-
arch/x86/include/asm/kvm.h | 1 +
arch/x86/kvm/mmu.c | 10 ++++
arch/x86/kvm/x86.c | 1 +
include/linux/kvm.h | 6 ++-
virt/kvm/kvm_main.c | 84 ++++++++++++++++++++++++++++--------
6 files changed, 89 insertions(+), 23 deletions(-)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 310fe50..4b3d3f1 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -857,7 +857,8 @@ struct kvm_userspace_memory_region {
};
/* for kvm_memory_region::flags */
-#define KVM_MEM_LOG_DIRTY_PAGES 1UL
+#define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0)
+#define KVM_MEM_READONLY (1UL << 1)
This ioctl allows the user to create or modify a guest physical memory
slot. When changing an existing slot, it may be moved in the guest
@@ -873,9 +874,12 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
be identical. This allows large pages in the guest to be backed by large
pages in the host.
-The flags field supports just one flag, KVM_MEM_LOG_DIRTY_PAGES, which
+The flags field supports two flag, KVM_MEM_LOG_DIRTY_PAGES, which
instructs kvm to keep track of writes to memory within the slot. See
-the KVM_GET_DIRTY_LOG ioctl.
+the KVM_GET_DIRTY_LOG ioctl. Another flag is KVM_MEM_READONLY when the
+KVM_CAP_READONLY_MEM capability, it indicates the guest memory is read-only,
+that means, guest is only allowed to read it. Writes will be posted to
+userspace as KVM_EXIT_MMIO exits.
When the KVM_CAP_SYNC_MMU capability, changes in the backing of the memory
region are automatically reflected into the guest. For example, an mmap()
diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
index 246617e..521bf25 100644
--- a/arch/x86/include/asm/kvm.h
+++ b/arch/x86/include/asm/kvm.h
@@ -25,6 +25,7 @@
#define __KVM_HAVE_DEBUGREGS
#define __KVM_HAVE_XSAVE
#define __KVM_HAVE_XCRS
+#define __KVM_HAVE_READONLY_MEM
/* Architectural interrupt line count. */
#define KVM_NR_INTERRUPTS 256
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 13d3c69..d4eee8e 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2618,6 +2618,16 @@ static void kvm_send_hwpoison_signal(unsigned long address, struct task_struct *
static int kvm_handle_bad_page(struct kvm_vcpu *vcpu, gfn_t gfn, pfn_t pfn)
{
kvm_release_pfn_clean(pfn);
+
+ /*
+ * Do not cache the mmio info caused by writing the readonly gfn
+ * into the spte otherwise read access on readonly gfn also can
+ * caused mmio page fault and treat it as mmio access.
+ * Return 1 to tell kvm to emulate it.
+ */
+ if (is_readonly_fault_pfn(pfn))
+ return 1;
+
if (is_hwpoison_pfn(pfn)) {
kvm_send_hwpoison_signal(gfn_to_hva(vcpu->kvm, gfn), current);
return 0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8171836..46e13a1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2153,6 +2153,7 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_GET_TSC_KHZ:
case KVM_CAP_PCI_2_3:
case KVM_CAP_KVMCLOCK_CTRL:
+ case KVM_CAP_READONLY_MEM:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index dc3aa2a..94867d0 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -102,7 +102,8 @@ struct kvm_userspace_memory_region {
};
/* for kvm_memory_region::flags */
-#define KVM_MEM_LOG_DIRTY_PAGES 1UL
+#define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0)
+#define KVM_MEM_READONLY (1UL << 1)
/* for KVM_IRQ_LINE */
struct kvm_irq_level {
@@ -617,6 +618,9 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_PPC_GET_SMMU_INFO 78
#define KVM_CAP_S390_COW 79
#define KVM_CAP_PPC_ALLOC_HTAB 80
+#ifdef __KVM_HAVE_READONLY_MEM
+#define KVM_CAP_READONLY_MEM 81
+#endif
#ifdef KVM_CAP_IRQ_ROUTING
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c056736..50e18c0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -694,7 +694,13 @@ void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new)
static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
{
- if (mem->flags & ~KVM_MEM_LOG_DIRTY_PAGES)
+ u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
+
+#ifdef KVM_CAP_READONLY_MEM
+ valid_flags |= KVM_MEM_READONLY;
+#endif
+
+ if (mem->flags & ~valid_flags)
return -EINVAL;
return 0;
@@ -1052,18 +1058,32 @@ out:
return size;
}
-static unsigned long gfn_to_hva_many(struct kvm_memory_slot *slot, gfn_t gfn,
- gfn_t *nr_pages)
+static bool memslot_is_readonly(struct kvm_memory_slot *slot)
+{
+ return slot->flags & KVM_MEM_READONLY;
+}
+
+static unsigned long __gfn_to_hva_many(struct kvm_memory_slot *slot, gfn_t gfn,
+ gfn_t *nr_pages, bool write)
{
if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
return bad_hva();
+ if (memslot_is_readonly(slot) && write)
+ return readonly_bad_hva();
+
if (nr_pages)
*nr_pages = slot->npages - (gfn - slot->base_gfn);
return gfn_to_hva_memslot(slot, gfn);
}
+static unsigned long gfn_to_hva_many(struct kvm_memory_slot *slot, gfn_t gfn,
+ gfn_t *nr_pages)
+{
+ return __gfn_to_hva_many(slot, gfn, nr_pages, true);
+}
+
unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
{
return gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, NULL);
@@ -1076,7 +1096,7 @@ EXPORT_SYMBOL_GPL(gfn_to_hva);
*/
static unsigned long gfn_to_hva_read(struct kvm *kvm, gfn_t gfn)
{
- return gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, NULL);
+ return __gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, NULL, false);
}
static int kvm_read_hva(void *data, void __user *hva, int len)
@@ -1201,6 +1221,17 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
return npages;
}
+static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault)
+{
+ if (unlikely(!(vma->vm_flags & VM_READ)))
+ return false;
+
+ if (write_fault && (unlikely(!(vma->vm_flags & VM_WRITE))))
+ return false;
+
+ return true;
+}
+
/*
* Pin guest page in memory and return its pfn.
* @addr: host virtual address which maps memory to the guest
@@ -1225,8 +1256,6 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
/* we can do it either atomically or asynchronously, not both */
BUG_ON(atomic && async);
- BUG_ON(!write_fault && !writable);
-
if (hva_to_pfn_fast(addr, atomic, async, write_fault, writable, &pfn))
return pfn;
@@ -1254,7 +1283,7 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
vma->vm_pgoff;
BUG_ON(!kvm_is_mmio_pfn(pfn));
} else {
- if (async && (vma->vm_flags & VM_WRITE))
+ if (async && vma_is_valid(vma, write_fault))
*async = true;
pfn = get_fault_pfn();
}
@@ -1264,21 +1293,41 @@ exit:
return pfn;
}
-static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic, bool *async,
- bool write_fault, bool *writable)
+static pfn_t
+__gfn_to_pfn_memslot(struct kvm_memory_slot *slot, gfn_t gfn, bool atomic,
+ bool *async, bool write_fault, bool *writable)
{
- unsigned long addr;
+ unsigned long addr = __gfn_to_hva_many(slot, gfn, NULL, write_fault);
- if (async)
- *async = false;
+ if (kvm_is_readonly_bad_hva(addr))
+ return get_readonly_fault_pfn();
- addr = gfn_to_hva(kvm, gfn);
if (kvm_is_error_hva(addr)) {
get_page(bad_page);
return page_to_pfn(bad_page);
}
- return hva_to_pfn(addr, atomic, async, write_fault, writable);
+ /* Do not map writable pfn in the readonly memslot. */
+ if (writable && memslot_is_readonly(slot))
+ writable = NULL;
+
+ return hva_to_pfn(addr, atomic, async, write_fault,
+ writable);
+}
+
+
+static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic, bool *async,
+ bool write_fault, bool *writable)
+{
+ struct kvm_memory_slot *slot;
+
+ if (async)
+ *async = false;
+
+ slot = gfn_to_memslot(kvm, gfn);
+
+ return __gfn_to_pfn_memslot(slot, gfn, atomic, async, write_fault,
+ writable);
}
pfn_t gfn_to_pfn_atomic(struct kvm *kvm, gfn_t gfn)
@@ -1309,15 +1358,12 @@ EXPORT_SYMBOL_GPL(gfn_to_pfn_prot);
pfn_t gfn_to_pfn_memslot(struct kvm_memory_slot *slot, gfn_t gfn)
{
- unsigned long addr = gfn_to_hva_memslot(slot, gfn);
- return hva_to_pfn(addr, false, NULL, true, NULL);
+ return __gfn_to_pfn_memslot(slot, gfn, false, NULL, true, NULL);
}
pfn_t gfn_to_pfn_memslot_atomic(struct kvm_memory_slot *slot, gfn_t gfn)
{
- unsigned long addr = gfn_to_hva_memslot(slot, gfn);
-
- return hva_to_pfn(addr, true, NULL, true, NULL);
+ return __gfn_to_pfn_memslot(slot, gfn, true, NULL, true, NULL);
}
EXPORT_SYMBOL_GPL(gfn_to_pfn_memslot_atomic);
--
1.7.7.6
--
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