diff options
| author | Chang S. Bae <chang.seok.bae@intel.com> | 2023-01-20 16:19:00 -0800 |
|---|---|---|
| committer | Dave Hansen <dave.hansen@linux.intel.com> | 2023-03-22 13:08:02 -0700 |
| commit | 5fbff260755750559aa12a30f6fa7f8a863666f1 (patch) | |
| tree | ce240b422a732435a688d446b5ad845ddb0478b1 | |
| parent | 7f9daaf59e14d62b29b6f4ca743e17bf96ff42ae (diff) | |
| download | lwn-5fbff260755750559aa12a30f6fa7f8a863666f1.tar.gz lwn-5fbff260755750559aa12a30f6fa7f8a863666f1.zip | |
Documentation/x86: Explain the state component permission for guests
Commit 980fe2fddcff ("x86/fpu: Extend fpu_xstate_prctl() with guest
permissions") extends a couple of arch_prctl(2) options for VCPU threads.
Add description for them.
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Yang Zhong <yang.zhong@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/all/20230121001900.14900-5-chang.seok.bae%40intel.com
| -rw-r--r-- | Documentation/x86/xstate.rst | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/Documentation/x86/xstate.rst b/Documentation/x86/xstate.rst index 23b1c9f3efb2..ae5c69e48b11 100644 --- a/Documentation/x86/xstate.rst +++ b/Documentation/x86/xstate.rst @@ -143,3 +143,32 @@ entry if the feature is in its initial configuration. This differs from non-dynamic features which are always written regardless of their configuration. Signal handlers can examine the XSAVE buffer's XSTATE_BV field to determine if a features was written. + +Dynamic features for virtual machines +------------------------------------- + +The permission for the guest state component needs to be managed separately +from the host, as they are exclusive to each other. A coupled of options +are extended to control the guest permission: + +-ARCH_GET_XCOMP_GUEST_PERM + + arch_prctl(ARCH_GET_XCOMP_GUEST_PERM, &features); + + ARCH_GET_XCOMP_GUEST_PERM is a variant of ARCH_GET_XCOMP_PERM. So it + provides the same semantics and functionality but for the guest + components. + +-ARCH_REQ_XCOMP_GUEST_PERM + + arch_prctl(ARCH_REQ_XCOMP_GUEST_PERM, feature_nr); + + ARCH_REQ_XCOMP_GUEST_PERM is a variant of ARCH_REQ_XCOMP_PERM. It has the + same semantics for the guest permission. While providing a similar + functionality, this comes with a constraint. Permission is frozen when the + first VCPU is created. Any attempt to change permission after that point + is going to be rejected. So, the permission has to be requested before the + first VCPU creation. + +Note that some VMMs may have already established a set of supported state +components. These options are not presumed to support any particular VMM. |