On Wed, 2022-12-14 at 10:19 +0100, Thomas Huth wrote:
On 13/12/2022 17.53, Janis Schoetterl-Glausch wrote:
User space can use the MEM_OP ioctl to make storage key checked reads and writes to the guest, however, it has no way of performing atomic, key checked, accesses to the guest. Extend the MEM_OP ioctl in order to allow for this, by adding a cmpxchg mode. For now, support this mode for absolute accesses only.
This mode can be use, for example, to set the device-state-change indicator and the adapter-local-summary indicator atomically.
Signed-off-by: Janis Schoetterl-Glausch scgl@linux.ibm.com
include/uapi/linux/kvm.h | 7 +++ arch/s390/kvm/gaccess.h | 3 ++ arch/s390/kvm/gaccess.c | 102 +++++++++++++++++++++++++++++++++++++++ arch/s390/kvm/kvm-s390.c | 39 ++++++++++++++- 4 files changed, 149 insertions(+), 2 deletions(-)
[...]
@@ -2714,12 +2721,19 @@ static bool access_key_invalid(u8 access_key) static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) { void __user *uaddr = (void __user *)mop->buf;
- void __user *old_addr = (void __user *)mop->old_addr;
- union {
__uint128_t quad;char raw[sizeof(__uint128_t)];- } old = { .quad = 0}, new = { .quad = 0 };
- unsigned int off_in_quad = sizeof(new) - mop->size; u64 supported_flags; void *tmpbuf = NULL; int r, srcu_idx;
supported_flags = KVM_S390_MEMOP_F_SKEY_PROTECTION
| KVM_S390_MEMOP_F_CHECK_ONLY;
| KVM_S390_MEMOP_F_CHECK_ONLY| KVM_S390_MEMOP_F_CMPXCHG;@@ -2741,6 +2755,19 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) } else { mop->key = 0; }
- if (mop->flags & KVM_S390_MEMOP_F_CMPXCHG) {
/** This validates off_in_quad. Checking that size is a power* of two is not necessary, as cmpxchg_guest_abs_with_key* takes care of that*/if (mop->size > sizeof(new))return -EINVAL;I'd maybe add a check for mop->op == KVM_S390_MEMOP_ABSOLUTE_WRITE here, since calling the _READ function with the F_CMPXCHG flag set does not make too much sense.
Good point.
Anyway, patch looks good to me, so with or without that additional check: Reviewed-by: Thomas Huth thuth@redhat.com
Thanks!
if (copy_from_user(&new.raw[off_in_quad], uaddr, mop->size))return -EFAULT;if (copy_from_user(&old.raw[off_in_quad], old_addr, mop->size))return -EFAULT;- } if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) { tmpbuf = vmalloc(mop->size); if (!tmpbuf)
@@ -2771,6 +2798,14 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) case KVM_S390_MEMOP_ABSOLUTE_WRITE: { if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) { r = check_gpa_range(kvm, mop->gaddr, mop->size, GACC_STORE, mop->key);
} else if (mop->flags & KVM_S390_MEMOP_F_CMPXCHG) {r = cmpxchg_guest_abs_with_key(kvm, mop->gaddr, mop->size,&old.quad, new.quad, mop->key);if (r == 1) {r = KVM_S390_MEMOP_R_NO_XCHG;if (copy_to_user(old_addr, &old.raw[off_in_quad], mop->size))r = -EFAULT;}