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KVM: s390: Add capability that forwards operation exceptions

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Setting KVM_CAP_S390_USER_OPEREXEC will forward all operation
exceptions to user space. This also includes the 0x0000 instructions
managed by KVM_CAP_S390_USER_INSTR0. It's helpful if user space wants
to emulate instructions which do not (yet) have an opcode.

While we're at it refine the documentation for
KVM_CAP_S390_USER_INSTR0.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
This commit is contained in:
Janosch Frank
2025-07-08 12:57:57 +00:00
parent 182a258b5e
commit 8e8678e740
7 changed files with 169 additions and 1 deletions
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17
Documentation/virt/kvm/api.rst
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@@ -7820,7 +7820,7 @@ where 0xff represents CPUs 0-7 in cluster 0.
:Architectures: s390
:Parameters: none
With this capability enabled, all illegal instructions 0x0000 (2 bytes) will
With this capability enabled, the illegal instruction 0x0000 (2 bytes) will
be intercepted and forwarded to user space. User space can use this
mechanism e.g. to realize 2-byte software breakpoints. The kernel will
not inject an operating exception for these instructions, user space has
@@ -8703,6 +8703,21 @@ This capability indicate to the userspace whether a PFNMAP memory region
can be safely mapped as cacheable. This relies on the presence of
force write back (FWB) feature support on the hardware.
7.45 KVM_CAP_S390_USER_OPEREXEC
-------------------------------
:Architectures: s390
:Parameters: none
When this capability is enabled KVM forwards all operation exceptions
that it doesn't handle itself to user space. This also includes the
0x0000 instructions managed by KVM_CAP_S390_USER_INSTR0. This is
helpful if user space wants to emulate instructions which are not
(yet) implemented in hardware.
This capability can be enabled dynamically even if VCPUs were already
created and are running.
8. Other capabilities.
======================