| Message ID | 20230206164602.138068-13-scgl@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg | expand |
On 2/6/23 17:46, 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 > 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> > --- > include/uapi/linux/kvm.h | 8 +++ > arch/s390/kvm/gaccess.h | 3 ++ > arch/s390/kvm/gaccess.c | 109 +++++++++++++++++++++++++++++++++++++++ > arch/s390/kvm/kvm-s390.c | 56 +++++++++++++++++++- > 4 files changed, 175 insertions(+), 1 deletion(-) > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 55155e262646..d2f30463c133 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -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 */ > diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h > index 9408d6cc8e2c..b320d12aa049 100644 > --- a/arch/s390/kvm/gaccess.h > +++ b/arch/s390/kvm/gaccess.h > @@ -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 > diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c > index 0243b6e38d36..3eb85f254881 100644 > --- a/arch/s390/kvm/gaccess.c > +++ b/arch/s390/kvm/gaccess.c > @@ -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 > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index 8a74b7b62ecf..5b77269e6536 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -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 @@ static int kvm_s390_vm_mem_op_abs(struct kvm *kvm, struct kvm_s390_mem_op *mop) > 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; > }
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 55155e262646..d2f30463c133 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -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 */ diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h index 9408d6cc8e2c..b320d12aa049 100644 --- a/arch/s390/kvm/gaccess.h +++ b/arch/s390/kvm/gaccess.h @@ -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 diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c index 0243b6e38d36..3eb85f254881 100644 --- a/arch/s390/kvm/gaccess.c +++ b/arch/s390/kvm/gaccess.c @@ -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 diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 8a74b7b62ecf..5b77269e6536 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -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 @@ static int kvm_s390_vm_mem_op_abs(struct kvm *kvm, struct kvm_s390_mem_op *mop) 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; }
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> --- include/uapi/linux/kvm.h | 8 +++ arch/s390/kvm/gaccess.h | 3 ++ arch/s390/kvm/gaccess.c | 109 +++++++++++++++++++++++++++++++++++++++ arch/s390/kvm/kvm-s390.c | 56 +++++++++++++++++++- 4 files changed, 175 insertions(+), 1 deletion(-)