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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
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@@ -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
------------------------