diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 9 | ||||
| -rw-r--r-- | Documentation/x86/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/x86/xstate.rst | 65 |
3 files changed, 75 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 43dc35fe5bc0..eb9a73ad91a0 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5497,6 +5497,15 @@ stifb= [HW] Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] + strict_sas_size= + [X86] + Format: <bool> + Enable or disable strict sigaltstack size checks + against the required signal frame size which + depends on the supported FPU features. This can + be used to filter out binaries which have + not yet been made aware of AT_MINSIGSTKSZ. + sunrpc.min_resvport= sunrpc.max_resvport= [NFS,SUNRPC] diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index 383048396336..f498f1d36cd3 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -37,3 +37,4 @@ x86-specific Documentation sgx features elf_auxvec + xstate diff --git a/Documentation/x86/xstate.rst b/Documentation/x86/xstate.rst new file mode 100644 index 000000000000..65de3f054ba5 --- /dev/null +++ b/Documentation/x86/xstate.rst @@ -0,0 +1,65 @@ +Using XSTATE features in user space applications +================================================ + +The x86 architecture supports floating-point extensions which are +enumerated via CPUID. Applications consult CPUID and use XGETBV to +evaluate which features have been enabled by the kernel XCR0. + +Up to AVX-512 and PKRU states, these features are automatically enabled by +the kernel if available. Features like AMX TILE_DATA (XSTATE component 18) +are enabled by XCR0 as well, but the first use of related instruction is +trapped by the kernel because by default the required large XSTATE buffers +are not allocated automatically. + +Using dynamically enabled XSTATE features in user space applications +-------------------------------------------------------------------- + +The kernel provides an arch_prctl(2) based mechanism for applications to +request the usage of such features. The arch_prctl(2) options related to +this are: + +-ARCH_GET_XCOMP_SUPP + + arch_prctl(ARCH_GET_XCOMP_SUPP, &features); + + ARCH_GET_XCOMP_SUPP stores the supported features in userspace storage of + type uint64_t. The second argument is a pointer to that storage. + +-ARCH_GET_XCOMP_PERM + + arch_prctl(ARCH_GET_XCOMP_PERM, &features); + + ARCH_GET_XCOMP_PERM stores the features for which the userspace process + has permission in userspace storage of type uint64_t. The second argument + is a pointer to that storage. + +-ARCH_REQ_XCOMP_PERM + + arch_prctl(ARCH_REQ_XCOMP_PERM, feature_nr); + + ARCH_REQ_XCOMP_PERM allows to request permission for a dynamically enabled + feature or a feature set. A feature set can be mapped to a facility, e.g. + AMX, and can require one or more XSTATE components to be enabled. + + The feature argument is the number of the highest XSTATE component which + is required for a facility to work. + +When requesting permission for a feature, the kernel checks the +availability. The kernel ensures that sigaltstacks in the process's tasks +are large enough to accommodate the resulting large signal frame. It +enforces this both during ARCH_REQ_XCOMP_SUPP and during any subsequent +sigaltstack(2) calls. If an installed sigaltstack is smaller than the +resulting sigframe size, ARCH_REQ_XCOMP_SUPP results in -ENOSUPP. Also, +sigaltstack(2) results in -ENOMEM if the requested altstack is too small +for the permitted features. + +Permission, when granted, is valid per process. Permissions are inherited +on fork(2) and cleared on exec(3). + +The first use of an instruction related to a dynamically enabled feature is +trapped by the kernel. The trap handler checks whether the process has +permission to use the feature. If the process has no permission then the +kernel sends SIGILL to the application. If the process has permission then +the handler allocates a larger xstate buffer for the task so the large +state can be context switched. In the unlikely cases that the allocation +fails, the kernel sends SIGSEGV. |