KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg
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
Janosch Frank
Родитель
701422b343
Коммит
3fd49805d1
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@ -1161,6 +1161,115 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
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return rc;
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}
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/**
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* cmpxchg_guest_abs_with_key() - Perform cmpxchg on guest absolute address.
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* @kvm: Virtual machine instance.
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* @gpa: Absolute guest address of the location to be changed.
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* @len: Operand length of the cmpxchg, required: 1 <= len <= 16. Providing a
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* non power of two will result in failure.
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* @old_addr: Pointer to old value. If the location at @gpa contains this value,
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* the exchange will succeed. After calling cmpxchg_guest_abs_with_key()
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* *@old_addr contains the value at @gpa before the attempt to
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* exchange the value.
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* @new: The value to place at @gpa.
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* @access_key: The access key to use for the guest access.
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* @success: output value indicating if an exchange occurred.
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*
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* Atomically exchange the value at @gpa by @new, if it contains *@old.
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* Honors storage keys.
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*
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* Return: * 0: successful exchange
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* * >0: a program interruption code indicating the reason cmpxchg could
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* not be attempted
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* * -EINVAL: address misaligned or len not power of two
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* * -EAGAIN: transient failure (len 1 or 2)
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* * -EOPNOTSUPP: read-only memslot (should never occur)
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*/
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int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len,
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__uint128_t *old_addr, __uint128_t new,
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u8 access_key, bool *success)
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{
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gfn_t gfn = gpa_to_gfn(gpa);
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struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
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bool writable;
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hva_t hva;
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int ret;
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if (!IS_ALIGNED(gpa, len))
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return -EINVAL;
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hva = gfn_to_hva_memslot_prot(slot, gfn, &writable);
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if (kvm_is_error_hva(hva))
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return PGM_ADDRESSING;
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/*
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* Check if it's a read-only memslot, even though that cannot occur
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* since those are unsupported.
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* Don't try to actually handle that case.
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*/
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if (!writable)
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return -EOPNOTSUPP;
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hva += offset_in_page(gpa);
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/*
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* The cmpxchg_user_key macro depends on the type of "old", so we need
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* a case for each valid length and get some code duplication as long
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* as we don't introduce a new macro.
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*/
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switch (len) {
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case 1: {
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u8 old;
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ret = cmpxchg_user_key((u8 __user *)hva, &old, *old_addr, new, access_key);
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*success = !ret && old == *old_addr;
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*old_addr = old;
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break;
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}
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case 2: {
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u16 old;
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ret = cmpxchg_user_key((u16 __user *)hva, &old, *old_addr, new, access_key);
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*success = !ret && old == *old_addr;
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*old_addr = old;
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break;
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}
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case 4: {
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u32 old;
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ret = cmpxchg_user_key((u32 __user *)hva, &old, *old_addr, new, access_key);
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*success = !ret && old == *old_addr;
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*old_addr = old;
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break;
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}
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case 8: {
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u64 old;
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ret = cmpxchg_user_key((u64 __user *)hva, &old, *old_addr, new, access_key);
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*success = !ret && old == *old_addr;
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*old_addr = old;
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break;
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}
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case 16: {
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__uint128_t old;
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ret = cmpxchg_user_key((__uint128_t __user *)hva, &old, *old_addr, new, access_key);
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*success = !ret && old == *old_addr;
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*old_addr = old;
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break;
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}
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default:
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return -EINVAL;
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}
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if (*success)
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mark_page_dirty_in_slot(kvm, slot, gfn);
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/*
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* Assume that the fault is caused by protection, either key protection
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* or user page write protection.
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*/
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if (ret == -EFAULT)
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ret = PGM_PROTECTION;
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return ret;
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}
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/**
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* guest_translate_address_with_key - translate guest logical into guest absolute address
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* @vcpu: virtual cpu
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@ -206,6 +206,9 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
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int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
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void *data, unsigned long len, enum gacc_mode mode);
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int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, __uint128_t *old,
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__uint128_t new, u8 access_key, bool *success);
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/**
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* write_guest_with_key - copy data from kernel space to guest space
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* @vcpu: virtual cpu
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@ -584,7 +584,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
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case KVM_CAP_S390_VCPU_RESETS:
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case KVM_CAP_SET_GUEST_DEBUG:
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case KVM_CAP_S390_DIAG318:
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case KVM_CAP_S390_MEM_OP_EXTENSION:
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r = 1;
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break;
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case KVM_CAP_SET_GUEST_DEBUG2:
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@ -598,6 +597,15 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
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case KVM_CAP_S390_MEM_OP:
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r = MEM_OP_MAX_SIZE;
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break;
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case KVM_CAP_S390_MEM_OP_EXTENSION:
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/*
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* Flag bits indicating which extensions are supported.
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* If r > 0, the base extension must also be supported/indicated,
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* in order to maintain backwards compatibility.
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*/
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r = KVM_S390_MEMOP_EXTENSION_CAP_BASE |
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KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG;
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break;
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case KVM_CAP_NR_VCPUS:
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case KVM_CAP_MAX_VCPUS:
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case KVM_CAP_MAX_VCPU_ID:
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@ -2832,6 +2840,50 @@ out_unlock:
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return r;
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}
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static int kvm_s390_vm_mem_op_cmpxchg(struct kvm *kvm, struct kvm_s390_mem_op *mop)
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{
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void __user *uaddr = (void __user *)mop->buf;
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void __user *old_addr = (void __user *)mop->old_addr;
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union {
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__uint128_t quad;
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char raw[sizeof(__uint128_t)];
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} old = { .quad = 0}, new = { .quad = 0 };
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unsigned int off_in_quad = sizeof(new) - mop->size;
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int r, srcu_idx;
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bool success;
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r = mem_op_validate_common(mop, KVM_S390_MEMOP_F_SKEY_PROTECTION);
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if (r)
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return r;
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/*
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* This validates off_in_quad. Checking that size is a power
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* of two is not necessary, as cmpxchg_guest_abs_with_key
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* takes care of that
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*/
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if (mop->size > sizeof(new))
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return -EINVAL;
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if (copy_from_user(&new.raw[off_in_quad], uaddr, mop->size))
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return -EFAULT;
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if (copy_from_user(&old.raw[off_in_quad], old_addr, mop->size))
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return -EFAULT;
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srcu_idx = srcu_read_lock(&kvm->srcu);
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if (kvm_is_error_gpa(kvm, mop->gaddr)) {
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r = PGM_ADDRESSING;
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goto out_unlock;
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}
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r = cmpxchg_guest_abs_with_key(kvm, mop->gaddr, mop->size, &old.quad,
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new.quad, mop->key, &success);
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if (!success && copy_to_user(old_addr, &old.raw[off_in_quad], mop->size))
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r = -EFAULT;
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out_unlock:
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srcu_read_unlock(&kvm->srcu, srcu_idx);
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return r;
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}
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static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
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{
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/*
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@ -2850,6 +2902,8 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
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case KVM_S390_MEMOP_ABSOLUTE_READ:
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case KVM_S390_MEMOP_ABSOLUTE_WRITE:
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return kvm_s390_vm_mem_op_abs(kvm, mop);
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case KVM_S390_MEMOP_ABSOLUTE_CMPXCHG:
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return kvm_s390_vm_mem_op_cmpxchg(kvm, mop);
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default:
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return -EINVAL;
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}
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@ -583,6 +583,8 @@ struct kvm_s390_mem_op {
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struct {
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__u8 ar; /* the access register number */
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__u8 key; /* access key, ignored if flag unset */
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__u8 pad1[6]; /* ignored */
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__u64 old_addr; /* ignored if cmpxchg flag unset */
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};
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__u32 sida_offset; /* offset into the sida */
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__u8 reserved[32]; /* ignored */
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@ -595,11 +597,17 @@ struct kvm_s390_mem_op {
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#define KVM_S390_MEMOP_SIDA_WRITE 3
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#define KVM_S390_MEMOP_ABSOLUTE_READ 4
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#define KVM_S390_MEMOP_ABSOLUTE_WRITE 5
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#define KVM_S390_MEMOP_ABSOLUTE_CMPXCHG 6
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/* flags for kvm_s390_mem_op->flags */
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#define KVM_S390_MEMOP_F_CHECK_ONLY (1ULL << 0)
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#define KVM_S390_MEMOP_F_INJECT_EXCEPTION (1ULL << 1)
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#define KVM_S390_MEMOP_F_SKEY_PROTECTION (1ULL << 2)
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/* flags specifying extension support via KVM_CAP_S390_MEM_OP_EXTENSION */
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#define KVM_S390_MEMOP_EXTENSION_CAP_BASE (1 << 0)
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#define KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG (1 << 1)
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/* for KVM_INTERRUPT */
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struct kvm_interrupt {
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/* in */
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