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KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg

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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
op. For now, support this op for absolute accesses only.

This op can be used, 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>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20230206164602.138068-13-scgl@linux.ibm.com
Message-Id: <20230206164602.138068-13-scgl@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
This commit is contained in:
Janis Schoetterl-Glausch 2023-02-06 17:46:00 +01:00 committed by Janosch Frank
parent 701422b343
commit 3fd49805d1
4 changed files with 175 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

109
arch/s390/kvm/gaccess.c
View File

@ -1161,6 +1161,115 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
return rc;
}
/**
* cmpxchg_guest_abs_with_key() - Perform cmpxchg on guest absolute address.
* @kvm: Virtual machine instance.
* @gpa: Absolute guest address of the location to be changed.
* @len: Operand length of the cmpxchg, required: 1 <= len <= 16. Providing a
* non power of two will result in failure.
* @old_addr: Pointer to old value. If the location at @gpa contains this value,
* the exchange will succeed. After calling cmpxchg_guest_abs_with_key()
* *@old_addr contains the value at @gpa before the attempt to
* exchange the value.
* @new: The value to place at @gpa.
* @access_key: The access key to use for the guest access.
* @success: output value indicating if an exchange occurred.
*
* Atomically exchange the value at @gpa by @new, if it contains *@old.
* Honors storage keys.
*
* Return: * 0: successful exchange
* * >0: a program interruption code indicating the reason cmpxchg could
* not be attempted
* * -EINVAL: address misaligned or len not power of two
* * -EAGAIN: transient failure (len 1 or 2)
* * -EOPNOTSUPP: read-only memslot (should never occur)
*/
int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len,
__uint128_t *old_addr, __uint128_t new,
u8 access_key, bool *success)
{
gfn_t gfn = gpa_to_gfn(gpa);
struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
bool writable;
hva_t hva;
int ret;
if (!IS_ALIGNED(gpa, len))
return -EINVAL;
hva = gfn_to_hva_memslot_prot(slot, gfn, &writable);
if (kvm_is_error_hva(hva))
return PGM_ADDRESSING;
/*
* Check if it's a read-only memslot, even though that cannot occur
* since those are unsupported.
* Don't try to actually handle that case.
*/
if (!writable)
return -EOPNOTSUPP;
hva += offset_in_page(gpa);
/*
* The cmpxchg_user_key macro depends on the type of "old", so we need
* a case for each valid length and get some code duplication as long
* as we don't introduce a new macro.
*/
switch (len) {
case 1: {
u8 old;
ret = cmpxchg_user_key((u8 __user *)hva, &old, *old_addr, new, access_key);
*success = !ret && old == *old_addr;
*old_addr = old;
break;
}
case 2: {
u16 old;
ret = cmpxchg_user_key((u16 __user *)hva, &old, *old_addr, new, access_key);
*success = !ret && old == *old_addr;
*old_addr = old;
break;
}
case 4: {
u32 old;
ret = cmpxchg_user_key((u32 __user *)hva, &old, *old_addr, new, access_key);
*success = !ret && old == *old_addr;
*old_addr = old;
break;
}
case 8: {
u64 old;
ret = cmpxchg_user_key((u64 __user *)hva, &old, *old_addr, new, access_key);
*success = !ret && old == *old_addr;
*old_addr = old;
break;
}
case 16: {
__uint128_t old;
ret = cmpxchg_user_key((__uint128_t __user *)hva, &old, *old_addr, new, access_key);
*success = !ret && old == *old_addr;
*old_addr = old;
break;
}
default:
return -EINVAL;
}
if (*success)
mark_page_dirty_in_slot(kvm, slot, gfn);
/*
* Assume that the fault is caused by protection, either key protection
* or user page write protection.
*/
if (ret == -EFAULT)
ret = PGM_PROTECTION;
return ret;
}
/**
* guest_translate_address_with_key - translate guest logical into guest absolute address
* @vcpu: virtual cpu

3
arch/s390/kvm/gaccess.h
View File

@ -206,6 +206,9 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
void *data, unsigned long len, enum gacc_mode mode);
int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, __uint128_t *old,
__uint128_t new, u8 access_key, bool *success);
/**
* write_guest_with_key - copy data from kernel space to guest space
* @vcpu: virtual cpu

56
arch/s390/kvm/kvm-s390.c
View File

@ -584,7 +584,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_S390_VCPU_RESETS:
case KVM_CAP_SET_GUEST_DEBUG:
case KVM_CAP_S390_DIAG318:
case KVM_CAP_S390_MEM_OP_EXTENSION:
r = 1;
break;
case KVM_CAP_SET_GUEST_DEBUG2:
@ -598,6 +597,15 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_S390_MEM_OP:
r = MEM_OP_MAX_SIZE;
break;
case KVM_CAP_S390_MEM_OP_EXTENSION:
/*
* Flag bits indicating which extensions are supported.
* If r > 0, the base extension must also be supported/indicated,
* in order to maintain backwards compatibility.
*/
r = KVM_S390_MEMOP_EXTENSION_CAP_BASE |
KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG;
break;
case KVM_CAP_NR_VCPUS:
case KVM_CAP_MAX_VCPUS:
case KVM_CAP_MAX_VCPU_ID:
@ -2832,6 +2840,50 @@ out_unlock:
return r;
}
static int kvm_s390_vm_mem_op_cmpxchg(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;
int r, srcu_idx;
bool success;
r = mem_op_validate_common(mop, KVM_S390_MEMOP_F_SKEY_PROTECTION);
if (r)
return r;
/*
* 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;
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;
srcu_idx = srcu_read_lock(&kvm->srcu);
if (kvm_is_error_gpa(kvm, mop->gaddr)) {
r = PGM_ADDRESSING;
goto out_unlock;
}
r = cmpxchg_guest_abs_with_key(kvm, mop->gaddr, mop->size, &old.quad,
new.quad, mop->key, &success);
if (!success && copy_to_user(old_addr, &old.raw[off_in_quad], mop->size))
r = -EFAULT;
out_unlock:
srcu_read_unlock(&kvm->srcu, srcu_idx);
return r;
}
static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
{
/*
@ -2850,6 +2902,8 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
case KVM_S390_MEMOP_ABSOLUTE_READ:
case KVM_S390_MEMOP_ABSOLUTE_WRITE:
return kvm_s390_vm_mem_op_abs(kvm, mop);
case KVM_S390_MEMOP_ABSOLUTE_CMPXCHG:
return kvm_s390_vm_mem_op_cmpxchg(kvm, mop);
default:
return -EINVAL;
}

8
include/uapi/linux/kvm.h
View File

@ -583,6 +583,8 @@ struct kvm_s390_mem_op {
struct {
__u8 ar; /* the access register number */
__u8 key; /* access key, ignored if flag unset */
__u8 pad1[6]; /* ignored */
__u64 old_addr; /* ignored if cmpxchg flag unset */
};
__u32 sida_offset; /* offset into the sida */
__u8 reserved[32]; /* ignored */
@ -595,11 +597,17 @@ struct kvm_s390_mem_op {
#define KVM_S390_MEMOP_SIDA_WRITE 3
#define KVM_S390_MEMOP_ABSOLUTE_READ 4
#define KVM_S390_MEMOP_ABSOLUTE_WRITE 5
#define KVM_S390_MEMOP_ABSOLUTE_CMPXCHG 6
/* 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)
#define KVM_S390_MEMOP_F_SKEY_PROTECTION (1ULL << 2)
/* flags specifying extension support via KVM_CAP_S390_MEM_OP_EXTENSION */
#define KVM_S390_MEMOP_EXTENSION_CAP_BASE (1 << 0)
#define KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG (1 << 1)
/* for KVM_INTERRUPT */
struct kvm_interrupt {
/* in */