kernel.git/arch/arm64/include/asm/fpsimd.h, branch linux-6.0.y

arm64/sme: Don't flush SVE register state when allocating SME storage

2022-08-23T10:29:11Z

Currently when taking a SME access trap we allocate storage for the SVE register state in order to be able to handle storage of streaming mode SVE. Due to the original usage in a purely SVE context the SVE register state allocation this also flushes the register state for SVE if storage was already allocated but in the SME context this is not desirable. For a SME access trap to be taken the task must not be in streaming mode so either there already is SVE register state present for regular SVE mode which would be corrupted or the task does not have TIF_SVE and the flush is redundant. Fix this by adding a flag to sve_alloc() indicating if we are in a SVE context and need to flush the state. Freshly allocated storage is always zeroed either way. Fixes: 8bd7f91c03d8 ("arm64/sme: Implement traps and syscall handling for SME") Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220817182324.638214-4-broonie@kernel.org Signed-off-by: Will Deacon

arm64/sme: Remove _EL0 from name of SVCR - FIXME sysreg.h

2022-05-16T18:50:20Z

The defines for SVCR call it SVCR_EL0 however the architecture calls the register SVCR with no _EL0 suffix. In preparation for generating the sysreg definitions rename to match the architecture, no functional change. Signed-off-by: Mark Brown Link: https://lore.kernel.org/r/20220510161208.631259-6-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Standardise bitfield names for SVCR

2022-05-16T18:50:20Z

The bitfield definitions for SVCR have a SYS_ added to the names of the constant which will be a problem for automatic generation. Remove the prefixes, no functional change. Signed-off-by: Mark Brown Link: https://lore.kernel.org/r/20220510161208.631259-5-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: More sensibly define the size for the ZA register set

2022-05-06T17:24:19Z

Since the vector length configuration mechanism is identical between SVE and SME we share large elements of the code including the definition for the maximum vector length. Unfortunately when we were defining the ABI for SVE we included not only the actual maximum vector length of 2048 bits but also the value possible if all the bits reserved in the architecture for expansion of the LEN field were used, 16384 bits. This starts creating problems if we try to allocate anything for the ZA matrix based on the maximum possible vector length, as we do for the regset used with ptrace during the process of generating a core dump. While the maximum potential size for ZA with the current architecture is a reasonably managable 64K with the higher reserved limit ZA would be 64M which leads to entirely reasonable complaints from the memory management code when we try to allocate a buffer of that size. Avoid these issues by defining the actual maximum vector length for the architecture and using it for the SME regsets. Also use the full ZA_PT_SIZE() with the header rather than just the actual register payload when specifying the size, fixing support for the largest vector lengths now that we have this new, lower define. With the SVE maximum this did not cause problems due to the extra headroom we had. While we're at it add a comment clarifying why even though ZA is a single register we tell the regset code that it is a multi-register regset. Reported-by: Qian Cai Signed-off-by: Mark Brown Tested-by: Naresh Kamboju Link: https://lore.kernel.org/r/20220505221517.1642014-1-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement ptrace support for streaming mode SVE registers

2022-04-22T17:51:15Z

The streaming mode SVE registers are represented using the same data structures as for SVE but since the vector lengths supported and in use may not be the same as SVE we represent them with a new type NT_ARM_SSVE. Unfortunately we only have a single 16 bit reserved field available in the header so there is no space to fit the current and maximum vector length for both standard and streaming SVE mode without redefining the structure in a way the creates a complicatd and fragile ABI. Since FFR is not present in streaming mode it is read and written as zero. Setting NT_ARM_SSVE registers will put the task into streaming mode, similarly setting NT_ARM_SVE registers will exit it. Reads that do not correspond to the current mode of the task will return the header with no register data. For compatibility reasons on write setting no flag for the register type will be interpreted as setting SVE registers, though users can provide no register data as an alternative mechanism for doing so. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-21-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement traps and syscall handling for SME

2022-04-22T17:51:05Z

By default all SME operations in userspace will trap. When this happens we allocate storage space for the SME register state, set up the SVE registers and disable traps. We do not need to initialize ZA since the architecture guarantees that it will be zeroed when enabled and when we trap ZA is disabled. On syscall we exit streaming mode if we were previously in it and ensure that all but the lower 128 bits of the registers are zeroed while preserving the state of ZA. This follows the aarch64 PCS for SME, ZA state is preserved over a function call and streaming mode is exited. Since the traps for SME do not distinguish between streaming mode SVE and ZA usage if ZA is in use rather than reenabling traps we instead zero the parts of the SVE registers not shared with FPSIMD and leave SME enabled, this simplifies handling SME traps. If ZA is not in use then we reenable SME traps and fall through to normal handling of SVE. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-17-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement ZA context switching

2022-04-22T17:51:02Z

Allocate space for storing ZA on first access to SME and use that to save and restore ZA state when context switching. We do this by using the vector form of the LDR and STR ZA instructions, these do not require streaming mode and have implementation recommendations that they avoid contention issues in shared SMCU implementations. Since ZA is architecturally guaranteed to be zeroed when enabled we do not need to explicitly zero ZA, either we will be restoring from a saved copy or trapping on first use of SME so we know that ZA must be disabled. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-16-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement streaming SVE context switching

2022-04-22T17:51:00Z

When in streaming mode we need to save and restore the streaming mode SVE register state rather than the regular SVE register state. This uses the streaming mode vector length and omits FFR but is otherwise identical, if TIF_SVE is enabled when we are in streaming mode then streaming mode takes precedence. This does not handle use of streaming SVE state with KVM, ptrace or signals. This will be updated in further patches. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-15-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement SVCR context switching

2022-04-22T17:50:58Z

In SME the use of both streaming SVE mode and ZA are tracked through PSTATE.SM and PSTATE.ZA, visible through the system register SVCR. In order to context switch the floating point state for SME we need to context switch the contents of this register as part of context switching the floating point state. Since changing the vector length exits streaming SVE mode and disables ZA we also make sure we update SVCR appropriately when setting vector length, and similarly ensure that new threads have streaming SVE mode and ZA disabled. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-14-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement vector length configuration prctl()s

2022-04-22T17:50:54Z

As for SVE provide a prctl() interface which allows processes to configure their SME vector length. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-12-broonie@kernel.org Signed-off-by: Catalin Marinas