KVM: Simply gfn_to_page()

Mapping a guest page to a host page is a common operation.  Currently,
one has first to find the memory slot where the page belongs (gfn_to_memslot),
then locate the page itself (gfn_to_page()).

This is clumsy, and also won't work well with memory aliases.  So simplify
gfn_to_page() not to require memory slot translation first, and instead do it
internally.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 25 insertions, 20 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 33eade7e237c..a0ec5dda3305 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -420,12 +420,12 @@ static int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3)
         u64 pdpte;
         u64 *pdpt;
         int ret;
-        struct kvm_memory_slot *memslot;
+        struct page *page;
 
         spin_lock(&vcpu->kvm->lock);
-        memslot = gfn_to_memslot(vcpu->kvm, pdpt_gfn);
-        /* FIXME: !memslot - emulate? 0xff? */
-        pdpt = kmap_atomic(gfn_to_page(memslot, pdpt_gfn), KM_USER0);
+        page = gfn_to_page(vcpu->kvm, pdpt_gfn);
+        /* FIXME: !page - emulate? 0xff? */
+        pdpt = kmap_atomic(page, KM_USER0);
 
         ret = 1;
         for (i = 0; i < 4; ++i) {
@@ -861,6 +861,17 @@ struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
 }
 EXPORT_SYMBOL_GPL(gfn_to_memslot);
 
+struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
+{
+        struct kvm_memory_slot *slot;
+
+        slot = gfn_to_memslot(kvm, gfn);
+        if (!slot)
+                return NULL;
+        return slot->phys_mem[gfn - slot->base_gfn];
+}
+EXPORT_SYMBOL_GPL(gfn_to_page);
+
 void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
 {
         int i;
@@ -899,20 +910,20 @@ static int emulator_read_std(unsigned long addr,
                 unsigned offset = addr & (PAGE_SIZE-1);
                 unsigned tocopy = min(bytes, (unsigned)PAGE_SIZE - offset);
                 unsigned long pfn;
-                struct kvm_memory_slot *memslot;
-                void *page;
+                struct page *page;
+                void *page_virt;
 
                 if (gpa == UNMAPPED_GVA)
                         return X86EMUL_PROPAGATE_FAULT;
                 pfn = gpa >> PAGE_SHIFT;
-                memslot = gfn_to_memslot(vcpu->kvm, pfn);
-                if (!memslot)
+                page = gfn_to_page(vcpu->kvm, pfn);
+                if (!page)
                         return X86EMUL_UNHANDLEABLE;
-                page = kmap_atomic(gfn_to_page(memslot, pfn), KM_USER0);
+                page_virt = kmap_atomic(page, KM_USER0);
 
-                memcpy(data, page + offset, tocopy);
+                memcpy(data, page_virt + offset, tocopy);
 
-                kunmap_atomic(page, KM_USER0);
+                kunmap_atomic(page_virt, KM_USER0);
 
                 bytes -= tocopy;
                 data += tocopy;
@@ -963,16 +974,14 @@ static int emulator_read_emulated(unsigned long addr,
 static int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
                                unsigned long val, int bytes)
 {
-        struct kvm_memory_slot *m;
         struct page *page;
         void *virt;
 
         if (((gpa + bytes - 1) >> PAGE_SHIFT) != (gpa >> PAGE_SHIFT))
                 return 0;
-        m = gfn_to_memslot(vcpu->kvm, gpa >> PAGE_SHIFT);
-        if (!m)
+        page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
+        if (!page)
                 return 0;
-        page = gfn_to_page(m, gpa >> PAGE_SHIFT);
         kvm_mmu_pre_write(vcpu, gpa, bytes);
         mark_page_dirty(vcpu->kvm, gpa >> PAGE_SHIFT);
         virt = kmap_atomic(page, KM_USER0);
@@ -2516,15 +2525,11 @@ static struct page *kvm_vm_nopage(struct vm_area_struct *vma,
 {
         struct kvm *kvm = vma->vm_file->private_data;
         unsigned long pgoff;
-        struct kvm_memory_slot *slot;
         struct page *page;
 
         *type = VM_FAULT_MINOR;
         pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
-        slot = gfn_to_memslot(kvm, pgoff);
-        if (!slot)
-                return NOPAGE_SIGBUS;
-        page = gfn_to_page(slot, pgoff);
+        page = gfn_to_page(kvm, pgoff);
         if (!page)
                 return NOPAGE_SIGBUS;
         get_page(page);