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KVM: s390: Add MEMOP ioctls for reading/writing guest memory

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On s390, we've got to make sure to hold the IPTE lock while accessing
logical memory. So let's add an ioctl for reading and writing logical
memory to provide this feature for userspace, too.
The maximum transfer size of this call is limited to 64kB to prevent
that the guest can trigger huge copy_from/to_user transfers. QEMU
currently only requests up to one or two pages so far, so 16*4kB seems
to be a reasonable limit here.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
This commit is contained in:
Thomas Huth 2015-02-06 15:01:21 +01:00 committed by Christian Borntraeger
parent 664b497353
commit 41408c28f2
5 changed files with 165 additions and 0 deletions
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46
Documentation/virtual/kvm/api.txt
View File

@ -2716,6 +2716,52 @@ 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_S390_MEM_OP
Capability: KVM_CAP_S390_MEM_OP
Architectures: s390
Type: vcpu ioctl
Parameters: struct kvm_s390_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 logical (virtual) memory of a VPCU.
Parameters are specified via the following structure:
struct kvm_s390_mem_op {
__u64 gaddr; /* the guest address */
__u64 flags; /* flags */
__u32 size; /* amount of bytes */
__u32 op; /* type of operation */
__u64 buf; /* buffer in userspace */
__u8 ar; /* the access register number */
__u8 reserved[31]; /* should be set to 0 */
};
The type of operation is specified in the "op" field. It is either
KVM_S390_MEMOP_LOGICAL_READ for reading from logical memory space or
KVM_S390_MEMOP_LOGICAL_WRITE for writing to logical memory space. The
KVM_S390_MEMOP_F_CHECK_ONLY flag can be set in the "flags" field to check
whether the corresponding memory access would create an access exception
(without touching 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.
This exception is also raised directly at the corresponding VCPU if the
flag KVM_S390_MEMOP_F_INJECT_EXCEPTION is set in the "flags" field.
The 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_S390_MEMOP_LOGICAL_READ, or where the data that should be written
is stored for a KVM_S390_MEMOP_LOGICAL_WRITE. "buf" is unused and can be NULL
when KVM_S390_MEMOP_F_CHECK_ONLY is specified. "ar" designates the access
register number to be used.
The "reserved" field is meant for future extensions. It is not used by
KVM with the currently defined set of flags.
5. The kvm_run structure
------------------------

22
arch/s390/kvm/gaccess.c
View File

@ -863,6 +863,28 @@ int guest_translate_address(struct kvm_vcpu *vcpu, unsigned long gva, ar_t ar,
return rc;
}
/**
* check_gva_range - test a range of guest virtual addresses for accessibility
*/
int check_gva_range(struct kvm_vcpu *vcpu, unsigned long gva, ar_t ar,
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, ar, &gpa, is_write);
gva += currlen;
length -= currlen;
}
ipte_unlock(vcpu);
return rc;
}
/**
* kvm_s390_check_low_addr_prot_real - check for low-address protection
* @gra: Guest real address

2
arch/s390/kvm/gaccess.h
View File

@ -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,
ar_t ar, unsigned long *gpa, int write);
int check_gva_range(struct kvm_vcpu *vcpu, unsigned long gva, ar_t ar,
unsigned long length, int is_write);
int access_guest(struct kvm_vcpu *vcpu, unsigned long ga, ar_t ar, void *data,
unsigned long len, int write);

74
arch/s390/kvm/kvm-s390.c
View File

@ -25,6 +25,7 @@
#include <linux/random.h>
#include <linux/slab.h>
#include <linux/timer.h>
#include <linux/vmalloc.h>
#include <asm/asm-offsets.h>
#include <asm/lowcore.h>
#include <asm/pgtable.h>
@ -38,6 +39,8 @@
#include "trace.h"
#include "trace-s390.h"
#define MEM_OP_MAX_SIZE 65536 /* Maximum transfer size for KVM_S390_MEM_OP */
#define VCPU_STAT(x) offsetof(struct kvm_vcpu, stat.x), KVM_STAT_VCPU
struct kvm_stats_debugfs_item debugfs_entries[] = {
@ -177,6 +180,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_S390_USER_SIGP:
r = 1;
break;
case KVM_CAP_S390_MEM_OP:
r = MEM_OP_MAX_SIZE;
break;
case KVM_CAP_NR_VCPUS:
case KVM_CAP_MAX_VCPUS:
r = KVM_MAX_VCPUS;
@ -2185,6 +2191,65 @@ 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_s390_mem_op *mop)
{
void __user *uaddr = (void __user *)mop->buf;
void *tmpbuf = NULL;
int r, srcu_idx;
const u64 supported_flags = KVM_S390_MEMOP_F_INJECT_EXCEPTION
| KVM_S390_MEMOP_F_CHECK_ONLY;
if (mop->flags & ~supported_flags)
return -EINVAL;
if (mop->size > MEM_OP_MAX_SIZE)
return -E2BIG;
if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) {
tmpbuf = vmalloc(mop->size);
if (!tmpbuf)
return -ENOMEM;
}
srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
switch (mop->op) {
case KVM_S390_MEMOP_LOGICAL_READ:
if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
r = check_gva_range(vcpu, mop->gaddr, mop->ar, mop->size, false);
break;
}
r = read_guest(vcpu, mop->gaddr, mop->ar, tmpbuf, mop->size);
if (r == 0) {
if (copy_to_user(uaddr, tmpbuf, mop->size))
r = -EFAULT;
}
break;
case KVM_S390_MEMOP_LOGICAL_WRITE:
if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) {
r = check_gva_range(vcpu, mop->gaddr, mop->ar, mop->size, true);
break;
}
if (copy_from_user(tmpbuf, uaddr, mop->size)) {
r = -EFAULT;
break;
}
r = write_guest(vcpu, mop->gaddr, mop->ar, tmpbuf, mop->size);
break;
default:
r = -EINVAL;
}
srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
if (r > 0 && (mop->flags & KVM_S390_MEMOP_F_INJECT_EXCEPTION) != 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)
{
@ -2284,6 +2349,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = kvm_vcpu_ioctl_enable_cap(vcpu, &cap);
break;
}
case KVM_S390_MEM_OP: {
struct kvm_s390_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;
}

21
include/uapi/linux/kvm.h
View File

@ -365,6 +365,24 @@ struct kvm_translation {
__u8 pad[5];
};
/* for KVM_S390_MEM_OP */
struct kvm_s390_mem_op {
/* in */
__u64 gaddr; /* the guest address */
__u64 flags; /* flags */
__u32 size; /* amount of bytes */
__u32 op; /* type of operation */
__u64 buf; /* buffer in userspace */
__u8 ar; /* the access register number */
__u8 reserved[31]; /* should be set to 0 */
};
/* types for kvm_s390_mem_op->op */
#define KVM_S390_MEMOP_LOGICAL_READ 0
#define KVM_S390_MEMOP_LOGICAL_WRITE 1
/* flags for kvm_s390_mem_op->flags */
#define KVM_S390_MEMOP_F_CHECK_ONLY (1ULL << 0)
#define KVM_S390_MEMOP_F_INJECT_EXCEPTION (1ULL << 1)
/* for KVM_INTERRUPT */
struct kvm_interrupt {
/* in */
@ -761,6 +779,7 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_CHECK_EXTENSION_VM 105
#define KVM_CAP_S390_USER_SIGP 106
#define KVM_CAP_S390_VECTOR_REGISTERS 107
#define KVM_CAP_S390_MEM_OP 108
#ifdef KVM_CAP_IRQ_ROUTING
@ -1136,6 +1155,8 @@ 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_S390_MEM_OP */
#define KVM_S390_MEM_OP _IOW(KVMIO, 0xb1, struct kvm_s390_mem_op)
#define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
#define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)