| Message ID | 20221213165405.2953539-3-scgl@linux.ibm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg | expand |
On Tue, 13 Dec 2022 17:53:58 +0100 Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote: > Describe the semantics of the new KVM_S390_MEMOP_F_CMPXCHG flag for > absolute vm write memops which allows user space to perform (storage key > checked) cmpxchg operations on guest memory. > > Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com> > --- > Documentation/virt/kvm/api.rst | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index eee9f857a986..98f5a35088b8 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -3753,7 +3753,8 @@ The fields in each entry are defined as follows: > :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 > + 16 bit program exception code if the access causes such an exception s/$/,/ > + other code > 0xffff with special meaning s/$/./ with those two nits fixed: Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com> > > Read or write data from/to the VM's memory. > The KVM_CAP_S390_MEM_OP_EXTENSION capability specifies what functionality is > @@ -3771,6 +3772,8 @@ Parameters are specified via the following structure:: > struct { > __u8 ar; /* the access register number */ > __u8 key; /* access key, ignored if flag unset */ > + __u8 pad1[6]; /* ignored */ > + __u64 old_addr; /* ignored if flag unset */ > }; > __u32 sida_offset; /* offset into the sida */ > __u8 reserved[32]; /* ignored */ > @@ -3853,8 +3856,21 @@ Absolute accesses are permitted for non-protected guests only. > Supported flags: > * ``KVM_S390_MEMOP_F_CHECK_ONLY`` > * ``KVM_S390_MEMOP_F_SKEY_PROTECTION`` > + * ``KVM_S390_MEMOP_F_CMPXCHG`` > + > +The semantics of the flags common with logical accesses are as for logical > +accesses. > + > +For write accesses, the KVM_S390_MEMOP_F_CMPXCHG flag is supported if > +KVM_CAP_S390_MEM_OP_EXTENSION has flag KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG set. > +In this case, instead of doing an unconditional write, the access occurs > +only if the target location contains the value pointed to by "old_addr". > +This is performed as an atomic cmpxchg with the length specified by the "size" > +parameter. "size" must be a power of two up to and including 16. > +If the exchange did not take place because the target value doesn't match the > +old value, KVM_S390_MEMOP_R_NO_XCHG is returned. > +In this case the value "old_addr" points to is replaced by the target value. > > -The semantics of the flags are as for logical accesses. > > SIDA read/write: > ^^^^^^^^^^^^^^^^
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index eee9f857a986..98f5a35088b8 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -3753,7 +3753,8 @@ The fields in each entry are defined as follows: :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 + 16 bit program exception code if the access causes such an exception + other code > 0xffff with special meaning Read or write data from/to the VM's memory. The KVM_CAP_S390_MEM_OP_EXTENSION capability specifies what functionality is @@ -3771,6 +3772,8 @@ Parameters are specified via the following structure:: struct { __u8 ar; /* the access register number */ __u8 key; /* access key, ignored if flag unset */ + __u8 pad1[6]; /* ignored */ + __u64 old_addr; /* ignored if flag unset */ }; __u32 sida_offset; /* offset into the sida */ __u8 reserved[32]; /* ignored */ @@ -3853,8 +3856,21 @@ Absolute accesses are permitted for non-protected guests only. Supported flags: * ``KVM_S390_MEMOP_F_CHECK_ONLY`` * ``KVM_S390_MEMOP_F_SKEY_PROTECTION`` + * ``KVM_S390_MEMOP_F_CMPXCHG`` + +The semantics of the flags common with logical accesses are as for logical +accesses. + +For write accesses, the KVM_S390_MEMOP_F_CMPXCHG flag is supported if +KVM_CAP_S390_MEM_OP_EXTENSION has flag KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG set. +In this case, instead of doing an unconditional write, the access occurs +only if the target location contains the value pointed to by "old_addr". +This is performed as an atomic cmpxchg with the length specified by the "size" +parameter. "size" must be a power of two up to and including 16. +If the exchange did not take place because the target value doesn't match the +old value, KVM_S390_MEMOP_R_NO_XCHG is returned. +In this case the value "old_addr" points to is replaced by the target value. -The semantics of the flags are as for logical accesses. SIDA read/write: ^^^^^^^^^^^^^^^^
Describe the semantics of the new KVM_S390_MEMOP_F_CMPXCHG flag for absolute vm write memops which allows user space to perform (storage key checked) cmpxchg operations on guest memory. Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com> --- Documentation/virt/kvm/api.rst | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-)