KVM: Allow cross page reads and writes from cached translations.

commit 8f964525a121f2ff2df948dac908dcc65be21b5b upstream.

This patch adds support for kvm_gfn_to_hva_cache_init functions for
reads and writes that will cross a page.  If the range falls within
the same memslot, then this will be a fast operation.  If the range
is split between two memslots, then the slower kvm_read_guest and
kvm_write_guest are used.

Tested: Test against kvm_clock unit tests.

Signed-off-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b2d5baf86da651f10e209b224a1ef88a7455e275..15e79a613723a0aea1d036f7af1abbab152bb710 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1448,7 +1448,8 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
                return 0;
        }
 
-       if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa))
+       if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
+                                       sizeof(u32)))
                return 1;
 
        vcpu->arch.apf.send_user_only = !(data & KVM_ASYNC_PF_SEND_ALWAYS);
@@ -1530,12 +1531,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 
                gpa_offset = data & ~(PAGE_MASK | 1);
 
-               /* Check that the address is 32-byte aligned. */
-               if (gpa_offset & (sizeof(struct pvclock_vcpu_time_info) - 1))
-                       break;
-
                if (kvm_gfn_to_hva_cache_init(vcpu->kvm,
-                    &vcpu->arch.pv_time, data & ~1ULL))
+                    &vcpu->arch.pv_time, data & ~1ULL,
+                    sizeof(struct pvclock_vcpu_time_info)))
                        vcpu->arch.pv_time_enabled = false;
                else
                        vcpu->arch.pv_time_enabled = true;

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8663a267ae332d03b8bb0deef469eeec90e53b5f..8cd0f206dee019de7f3532c7c4475d12f906f6bc 100644 (file)
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -388,7 +388,7 @@ int kvm_write_guest(struct kvm *kvm, gpa_t gpa, const void *data,
 int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
                           void *data, unsigned long len);
 int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
-                             gpa_t gpa);
+                             gpa_t gpa, unsigned long len);
 int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len);
 int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len);
 struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn);

diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index fa7cc7244cbdbf019591f644e42622145c8dd28b..b0bcce0ddc95a531dd30c30e91a89c92e961b8d4 100644 (file)
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -71,6 +71,7 @@ struct gfn_to_hva_cache {
        u64 generation;
        gpa_t gpa;
        unsigned long hva;
+       unsigned long len;
        struct kvm_memory_slot *memslot;
 };
 

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 88dde44bc07b7985b791f6c1e215a3969c03323c..caa3bb158d2265e8a71206ecac1f56b199500bd4 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1375,20 +1375,38 @@ int kvm_write_guest(struct kvm *kvm, gpa_t gpa, const void *data,
 }
 
 int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
-                             gpa_t gpa)
+                             gpa_t gpa, unsigned long len)
 {
        struct kvm_memslots *slots = kvm_memslots(kvm);
        int offset = offset_in_page(gpa);
-       gfn_t gfn = gpa >> PAGE_SHIFT;
+       gfn_t start_gfn = gpa >> PAGE_SHIFT;
+       gfn_t end_gfn = (gpa + len - 1) >> PAGE_SHIFT;
+       gfn_t nr_pages_needed = end_gfn - start_gfn + 1;
+       gfn_t nr_pages_avail;
 
        ghc->gpa = gpa;
        ghc->generation = slots->generation;
-       ghc->memslot = __gfn_to_memslot(slots, gfn);
-       ghc->hva = gfn_to_hva_many(ghc->memslot, gfn, NULL);
-       if (!kvm_is_error_hva(ghc->hva))
+       ghc->len = len;
+       ghc->memslot = gfn_to_memslot(kvm, start_gfn);
+       ghc->hva = gfn_to_hva_many(ghc->memslot, start_gfn, &nr_pages_avail);
+       if (!kvm_is_error_hva(ghc->hva) && nr_pages_avail >= nr_pages_needed) {
                ghc->hva += offset;
-       else
-               return -EFAULT;
+       } else {
+               /*
+                * If the requested region crosses two memslots, we still
+                * verify that the entire region is valid here.
+                */
+               while (start_gfn <= end_gfn) {
+                       ghc->memslot = gfn_to_memslot(kvm, start_gfn);
+                       ghc->hva = gfn_to_hva_many(ghc->memslot, start_gfn,
+                                                  &nr_pages_avail);
+                       if (kvm_is_error_hva(ghc->hva))
+                               return -EFAULT;
+                       start_gfn += nr_pages_avail;
+               }
+               /* Use the slow path for cross page reads and writes. */
+               ghc->memslot = NULL;
+       }
 
        return 0;
 }
@@ -1400,8 +1418,13 @@ int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
        struct kvm_memslots *slots = kvm_memslots(kvm);
        int r;
 
+       BUG_ON(len > ghc->len);
+
        if (slots->generation != ghc->generation)
-               kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa);
+               kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa, ghc->len);
+
+       if (unlikely(!ghc->memslot))
+               return kvm_write_guest(kvm, ghc->gpa, data, len);
 
        if (kvm_is_error_hva(ghc->hva))
                return -EFAULT;