[Qemu-devel] [PATCH RFC 1/1] KVM: s390: Add MEMOP ioctl for reading/writing guest memory

[Thomas Huth]

On s390, we've got to make sure to hold the IPTE lock while accessing
virtual memory. So let's add an ioctl for reading and writing virtual
memory to provide this feature for userspace, too.

Signed-off-by: Thomas Huth <address@hidden>
Reviewed-by: Dominik Dingel <address@hidden>
Reviewed-by: David Hildenbrand <address@hidden>
---
 Documentation/virtual/kvm/api.txt |   44 +++++++++++++++++++++++++
 arch/s390/kvm/gaccess.c           |   22 +++++++++++++
 arch/s390/kvm/gaccess.h           |    2 +
 arch/s390/kvm/kvm-s390.c          |   63 +++++++++++++++++++++++++++++++++++++
 include/uapi/linux/kvm.h          |   21 ++++++++++++
 5 files changed, 152 insertions(+), 0 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt 
b/Documentation/virtual/kvm/api.txt
index b112efc..bf44b53 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2716,6 +2716,50 @@ The fields in each entry are defined as follows:
    eax, ebx, ecx, edx: the values returned by the cpuid instruction for
          this function/index combination
 
+4.89 KVM_GUEST_MEM_OP
+
+Capability: KVM_CAP_MEM_OP
+Architectures: s390
+Type: vcpu ioctl
+Parameters: struct kvm_guest_mem_op (in)
+Returns: = 0 on success,
+         < 0 on generic error (e.g. -EFAULT or -ENOMEM),
+         > 0 if an exception occurred while walking the page tables
+
+Read or write data from/to the virtual memory of a VPCU.
+
+Parameters are specified via the following structure:
+
+struct kvm_guest_mem_op {
+       __u64 gaddr;            /* the guest address */
+       __u64 flags;            /* arch specific flags */
+       __u32 size;             /* amount of bytes */
+       __u32 op;               /* type of operation */
+       __u64 buf;              /* buffer in userspace */
+       __u8 reserved[32];      /* should be set to 0 */
+};
+
+The type of operation is specified in the "op" field, either KVM_MEMOP_VIRTREAD
+for reading from memory, KVM_MEMOP_VIRTWRITE for writing to memory, or
+KVM_MEMOP_CHECKVIRTREAD or KVM_MEMOP_CHECKVIRTWRITE to check whether the
+corresponding memory access would create an access exception (without
+changing the data in the memory at the destination). In case an access
+exception occurred while walking the MMU tables of the guest, the ioctl
+returns a positive error number to indicate the type of exception. The
+exception is raised directly at the corresponding VCPU if the bit
+KVM_MEMOP_F_INJECT_EXC is set in the "flags" field.
+
+The logical (virtual) start address of the memory region has to be specified
+in the "gaddr" field, and the length of the region in the "size" field.
+"buf" is the buffer supplied by the userspace application where the read data
+should be written to for KVM_MEMOP_VIRTREAD, or where the data that should
+be written is stored for a KVM_MEMOP_VIRTWRITE. "buf" can be NULL for both
+CHECK operations.
+
+The "reserved" field is meant for future extensions. It must currently be
+set to 0.
+
+
 5. The kvm_run structure
 ------------------------
 
diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 8a1be90..d912362 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -697,6 +697,28 @@ int guest_translate_address(struct kvm_vcpu *vcpu, 
unsigned long gva,
 }
 
 /**
+ * check_gva_range - test a range of guest virtual addresses for accessibility
+ */
+int check_gva_range(struct kvm_vcpu *vcpu, unsigned long gva,
+                   unsigned long length, int is_write)
+{
+       unsigned long gpa;
+       unsigned long currlen;
+       int rc = 0;
+
+       ipte_lock(vcpu);
+       while (length > 0 && !rc) {
+               currlen = min(length, PAGE_SIZE - (gva % PAGE_SIZE));
+               rc = guest_translate_address(vcpu, gva, &gpa, is_write);
+               gva += currlen;
+               length -= currlen;
+       }
+       ipte_unlock(vcpu);
+
+       return rc;
+}
+
+/**
  * kvm_s390_check_low_addr_protection - check for low-address protection
  * @ga: Guest address
  *
diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h
index 0149cf1..268beb7 100644
--- a/arch/s390/kvm/gaccess.h
+++ b/arch/s390/kvm/gaccess.h
@@ -157,6 +157,8 @@ int read_guest_lc(struct kvm_vcpu *vcpu, unsigned long gra, 
void *data,
 
 int guest_translate_address(struct kvm_vcpu *vcpu, unsigned long gva,
                            unsigned long *gpa, int write);
+int check_gva_range(struct kvm_vcpu *vcpu, unsigned long gva,
+                   unsigned long length, int is_write);
 
 int access_guest(struct kvm_vcpu *vcpu, unsigned long ga, void *data,
                 unsigned long len, int write);
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index b2371c0..c80a640 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -168,6 +168,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
        case KVM_CAP_VM_ATTRIBUTES:
        case KVM_CAP_MP_STATE:
        case KVM_CAP_S390_USER_SIGP:
+       case KVM_CAP_MEM_OP:
                r = 1;
                break;
        case KVM_CAP_NR_VCPUS:
@@ -1886,6 +1887,59 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu 
*vcpu,
        return r;
 }
 
+static long kvm_s390_guest_mem_op(struct kvm_vcpu *vcpu,
+                                 struct kvm_guest_mem_op *mop)
+{
+       void __user *uaddr = (void __user *)mop->buf;
+       void *tmpbuf = NULL;
+       int r, srcu_idx;
+
+       if ((mop->flags & ~KVM_MEMOP_F_INJECT_EXC) != 0)
+               return -EINVAL;
+
+       if (mop->op == KVM_MEMOP_VIRTREAD || mop->op == KVM_MEMOP_VIRTWRITE) {
+               if (mop->size > 16 * PAGE_SIZE)
+                       return -E2BIG;
+               tmpbuf = vmalloc(mop->size);
+               if (!tmpbuf)
+                       return -ENOMEM;
+       }
+
+       srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+
+       switch (mop->op) {
+       case KVM_MEMOP_VIRTREAD:
+               r = read_guest(vcpu, mop->gaddr, tmpbuf, mop->size);
+               if (r == 0) {
+                       if (copy_to_user(uaddr, tmpbuf, mop->size))
+                               r = -EFAULT;
+               }
+               break;
+       case KVM_MEMOP_VIRTWRITE:
+               if (copy_from_user(tmpbuf, uaddr, mop->size)) {
+                       r = -EFAULT;
+                       break;
+               }
+               r = write_guest(vcpu, mop->gaddr, tmpbuf, mop->size);
+               break;
+       case KVM_MEMOP_CHECKVIRTREAD:
+       case KVM_MEMOP_CHECKVIRTWRITE:
+               r = check_gva_range(vcpu, mop->gaddr, mop->size,
+                                   mop->op == KVM_MEMOP_CHECKVIRTWRITE);
+               break;
+       default:
+               r = -EINVAL;
+       }
+
+       srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
+
+       if (r > 0 && (mop->flags & KVM_MEMOP_F_INJECT_EXC) != 0)
+               kvm_s390_inject_prog_irq(vcpu, &vcpu->arch.pgm);
+
+       vfree(tmpbuf);
+       return r;
+}
+
 long kvm_arch_vcpu_ioctl(struct file *filp,
                         unsigned int ioctl, unsigned long arg)
 {
@@ -1985,6 +2039,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
                r = kvm_vcpu_ioctl_enable_cap(vcpu, &cap);
                break;
        }
+       case KVM_GUEST_MEM_OP: {
+               struct kvm_guest_mem_op mem_op;
+
+               if (copy_from_user(&mem_op, argp, sizeof(mem_op)) == 0)
+                       r = kvm_s390_guest_mem_op(vcpu, &mem_op);
+               else
+                       r = -EFAULT;
+               break;
+       }
        default:
                r = -ENOTTY;
        }
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 8055706..528a3d4 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -365,6 +365,24 @@ struct kvm_translation {
        __u8  pad[5];
 };
 
+/* for KVM_GUEST_MEM_OP */
+struct kvm_guest_mem_op {
+       /* in */
+       __u64 gaddr;            /* the guest address */
+       __u64 flags;            /* arch specific flags */
+       __u32 size;             /* amount of bytes */
+       __u32 op;               /* type of operation */
+       __u64 buf;              /* buffer in userspace */
+       __u8 reserved[32];      /* should be set to 0 */
+};
+/* types for kvm_guest_mem_op->op */
+#define KVM_MEMOP_VIRTREAD             0
+#define KVM_MEMOP_VIRTWRITE            1
+#define KVM_MEMOP_CHECKVIRTREAD                2
+#define KVM_MEMOP_CHECKVIRTWRITE       3
+/* flags for kvm_guest_mem_op->flags */
+#define KVM_MEMOP_F_INJECT_EXC 0x0001UL        /* Inject exception on faults */
+
 /* for KVM_INTERRUPT */
 struct kvm_interrupt {
        /* in */
@@ -760,6 +778,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_PPC_ENABLE_HCALL 104
 #define KVM_CAP_CHECK_EXTENSION_VM 105
 #define KVM_CAP_S390_USER_SIGP 106
+#define KVM_CAP_MEM_OP 107
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1135,6 +1154,8 @@ struct kvm_s390_ucas_mapping {
 #define KVM_ARM_VCPU_INIT        _IOW(KVMIO,  0xae, struct kvm_vcpu_init)
 #define KVM_ARM_PREFERRED_TARGET  _IOR(KVMIO,  0xaf, struct kvm_vcpu_init)
 #define KVM_GET_REG_LIST         _IOWR(KVMIO, 0xb0, struct kvm_reg_list)
+/* Available with KVM_CAP_MEM_OP */
+#define KVM_GUEST_MEM_OP         _IOW(KVMIO,  0xb1, struct kvm_guest_mem_op)
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU    (1 << 0)
 #define KVM_DEV_ASSIGN_PCI_2_3         (1 << 1)
-- 
1.7.1