Messages in this thread Patch in this message | | | From | "Chang S. Bae" <> | Subject | [PATCH v10 09/28] x86/fpu/xstate: Introduce helpers to manage the XSTATE buffer dynamically | Date | Wed, 25 Aug 2021 08:53:54 -0700 |
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The static XSTATE per-task buffer contains the extended register states -- but it is not expandable at runtime. Introduce runtime methods and a new fpu struct field to support the expansion.
fpu->state_mask indicates which state components are to be saved in the XSTATE buffer.
realloc_xstate_buffer() uses vzalloc(). If use of this mechanism grows to re-allocate buffers larger than 64KB, a more sophisticated allocation scheme that includes purpose-built reclaim capability might be justified.
Introduce a new helper -- calculate_xstate_buf_size_from_mask() to calculate the buffer size.
Also, use the new field and helper to initialize the buffer.
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> Reviewed-by: Len Brown <len.brown@intel.com> Cc: x86@kernel.org Cc: linux-kernel@vger.kernel.org --- Changes from v9: * Rename and simplify helpers. (Borislav Petkov) * Add and fix the code comment and the variable name. (Borislav Petkov) * Use cpu_feature_enabled() instead of boot_cpu_has(). (Borislav Petkov) * Use fpu->state_mask to ensure states to be written in copy_uabi_to_xstate() -- moved from Patch11. (Borislav Petkov)
Changes from v5: * Added to ensure XSAVES format with current in fpu_reset_fpstate() for new base code.
Changes from v3: * Updated code comments. (Borislav Petkov) * Used vzalloc() instead of vmalloc() with memset(). (Borislav Petkov) * Removed the max size check for >64KB. (Borislav Petkov) * Removed the allocation size check in the helper. (Borislav Petkov) * Switched the function description in the kernel-doc style. * Used them for buffer initialization -- moved from the next patch.
Changes from v2: * Updated the changelog with task->fpu removed. (Borislav Petkov) * Replaced 'area' with 'buffer' in the comments and the changelog. * Updated the code comments.
Changes from v1: * Removed unneeded interrupt masking (Andy Lutomirski) * Added vmalloc() error tracing (Dave Hansen, PeterZ, and Andy Lutomirski) --- arch/x86/include/asm/fpu/types.h | 7 ++ arch/x86/include/asm/fpu/xstate.h | 3 + arch/x86/kernel/fpu/core.c | 19 +++-- arch/x86/kernel/fpu/xstate.c | 123 ++++++++++++++++++++++++++++++ 4 files changed, 145 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index ad5cbf922e30..0cc9f6c5a10c 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -336,6 +336,13 @@ struct fpu { */ unsigned long avx512_timestamp; + /* + * @state_mask: + * + * The bitmap represents state components to be saved in ->state. + */ + u64 state_mask; + /* * @state: * diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h index c4a0914b7717..cbe19e05b5c9 100644 --- a/arch/x86/include/asm/fpu/xstate.h +++ b/arch/x86/include/asm/fpu/xstate.h @@ -153,7 +153,10 @@ struct fpu_xstate_buffer_config { extern struct fpu_xstate_buffer_config fpu_buf_cfg; +unsigned int calculate_xstate_buf_size_from_mask(u64 mask); void *get_xsave_addr(struct fpu *fpu, int xfeature_nr); +int realloc_xstate_buffer(struct fpu *fpu, u64 mask); +void free_xstate_buffer(struct fpu *fpu); int xfeature_size(int xfeature_nr); int copy_uabi_from_kernel_to_xstate(struct fpu *fpu, const void *kbuf); int copy_sigframe_from_user_to_xstate(struct fpu *fpu, const void __user *ubuf); diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 6b55b8c651f6..2941d03912db 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -236,9 +236,8 @@ void fpstate_init(struct fpu *fpu) if (likely(fpu)) { state = fpu->state; - /* The dynamic user states are not prepared yet. */ - mask = xfeatures_mask_all & ~xfeatures_mask_user_dynamic; - size = fpu_buf_cfg.min_size; + mask = fpu->state_mask; + size = calculate_xstate_buf_size_from_mask(fpu->state_mask); } else { state = &init_fpstate; mask = xfeatures_mask_all; @@ -274,14 +273,16 @@ int fpu_clone(struct task_struct *dst) if (!cpu_feature_enabled(X86_FEATURE_FPU)) return 0; + /* + * The child does not inherit the dynamic states. Thus, use the + * buffer embedded in struct task_struct, which has the minimum + * size. + */ + dst_fpu->state_mask = (xfeatures_mask_all & ~xfeatures_mask_user_dynamic); dst_fpu->state = &dst_fpu->__default_state; - /* * Don't let 'init optimized' areas of the XSAVE area * leak into the child task: - * - * The child does not inherit the dynamic states. So, - * the xstate buffer has the minimum size. */ memset(&dst_fpu->state->xsave, 0, fpu_buf_cfg.min_size); @@ -380,6 +381,10 @@ static void fpu_reset_fpstate(void) * flush_thread(). */ memcpy(fpu->state, &init_fpstate, init_fpstate_copy_size()); + /* Adjust the xstate buffer format for current. */ + if (cpu_feature_enabled(X86_FEATURE_XSAVES)) + fpstate_init_xstate(&fpu->state->xsave, fpu->state_mask); + set_thread_flag(TIF_NEED_FPU_LOAD); fpregs_unlock(); } diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 4496750208a8..f56db3f77282 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -10,6 +10,7 @@ #include <linux/pkeys.h> #include <linux/seq_file.h> #include <linux/proc_fs.h> +#include <linux/vmalloc.h> #include <asm/fpu/api.h> #include <asm/fpu/internal.h> @@ -19,6 +20,7 @@ #include <asm/tlbflush.h> #include <asm/cpufeature.h> +#include <asm/trace/fpu.h> /* * Although we spell it out in here, the Processor Trace @@ -76,6 +78,12 @@ static unsigned int xstate_comp_offsets[XFEATURE_MAX] __ro_after_init = { [ 0 ... XFEATURE_MAX - 1] = -1}; static unsigned int xstate_supervisor_only_offsets[XFEATURE_MAX] __ro_after_init = { [ 0 ... XFEATURE_MAX - 1] = -1}; +/* + * True if the buffer of the corresponding XFEATURE is located on the next 64 + * byte boundary. Otherwise, it follows the preceding component immediately. + */ +static bool xstate_64byte_aligned[XFEATURE_MAX] __ro_after_init = + { [ 0 ... XFEATURE_MAX - 1] = false}; struct fpu_xstate_buffer_config fpu_buf_cfg __ro_after_init; EXPORT_SYMBOL_GPL(fpu_buf_cfg); @@ -131,6 +139,58 @@ static bool xfeature_is_supervisor(int xfeature_nr) return ecx & 1; } +/** + * calculate_xstate_buf_size_from_mask - Calculate an xstate buffer size + * @mask: A bitmap to tell which components to be saved in the buffer. + * + * Available once those arrays for the offset, size, and alignment info are + * set up, by setup_xstate_features(). + * + * Returns: The buffer size + */ +unsigned int calculate_xstate_buf_size_from_mask(u64 mask) +{ + unsigned int size = FXSAVE_SIZE + XSAVE_HDR_SIZE; + int i, nr; + + if (!mask) + return 0; + + /* + * The minimum buffer size excludes the dynamic user state. When a + * task uses the state, the buffer can grow up to the max size. + */ + if (mask == (xfeatures_mask_all & ~xfeatures_mask_user_dynamic)) + return fpu_buf_cfg.min_size; + else if (mask == xfeatures_mask_all) + return fpu_buf_cfg.max_size; + + nr = fls64(mask) - 1; + if (nr < FIRST_EXTENDED_XFEATURE) + return size; + + /* + * Each state offset in the non-compacted format is fixed. Take the + * size from the last feature 'nr'. + */ + if (!cpu_feature_enabled(X86_FEATURE_XSAVES)) + return xstate_offsets[nr] + xstate_sizes[nr]; + + /* + * With the given mask, no relevant size is found so far. So, + * calculate it by summing up each state size. + */ + for (i = FIRST_EXTENDED_XFEATURE; i <= nr; i++) { + if (!(mask & BIT_ULL(i))) + continue; + + if (xstate_64byte_aligned[i]) + size = ALIGN(size, 64); + size += xstate_sizes[i]; + } + return size; +} + /* * Enable the extended processor state save/restore feature. * Called once per CPU onlining. @@ -202,6 +262,7 @@ static void __init setup_xstate_features(void) continue; xstate_offsets[i] = ebx; + xstate_64byte_aligned[i] = (ecx & 2) ? true : false; /* * In our xstate size checks, we assume that the highest-numbered @@ -805,6 +866,12 @@ void __init fpu__init_system_xstate(void) if (err) goto out_disable; + /* + * Initially, the FPU buffer used is the static one, without + * dynamic states. + */ + current->thread.fpu.state_mask = (xfeatures_mask_all & ~xfeatures_mask_user_dynamic); + /* * Update info used for ptrace frames; use standard-format size and no * supervisor xstates: @@ -995,6 +1062,60 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, } #endif /* ! CONFIG_ARCH_HAS_PKEYS */ +void free_xstate_buffer(struct fpu *fpu) +{ + vfree(fpu->state); +} + +/** + * realloc_xstate_buffer - Re-alloc a buffer with the size calculated from + * @mask. + * + * @fpu: A struct fpu * pointer + * @mask: The bitmap tells which components to be reserved in the new + * buffer. + * + * It deals with enlarging the xstate buffer with dynamic states. + * + * Use vzalloc() simply here. If the task with a vzalloc()-allocated buffer + * tends to terminate quickly, vfree()-induced IPIs may be a concern. + * Caching may be helpful for this. But the task with large state is likely + * to live longer. + * + * Also, this method does not shrink or reclaim the buffer. + * + * Returns 0 on success, -ENOMEM on allocation error. + */ +int realloc_xstate_buffer(struct fpu *fpu, u64 mask) +{ + union fpregs_state *state; + u64 state_mask; + + state_mask = fpu->state_mask | mask; + if ((state_mask & fpu->state_mask) == state_mask) + return 0; + + state = vzalloc(calculate_xstate_buf_size_from_mask(state_mask)); + if (!state) + return -ENOMEM; + + /* + * As long as the register state is intact, save the xstate in the + * new buffer at the next context switch or ptrace's context + * injection. + */ + if (cpu_feature_enabled(X86_FEATURE_XSAVES)) + fpstate_init_xstate(&state->xsave, state_mask); + + /* Free the old buffer */ + if (fpu->state != &fpu->__default_state) + free_xstate_buffer(fpu); + + fpu->state = state; + fpu->state_mask = state_mask; + return 0; +} + static void copy_feature(bool from_xstate, struct membuf *to, void *xstate, void *init_xstate, unsigned int size) { @@ -1147,6 +1268,8 @@ static int copy_uabi_to_xstate(struct fpu *fpu, const void *kbuf, if (validate_user_xstate_header(&hdr)) return -EINVAL; + hdr.xfeatures &= fpu->state_mask; + /* Validate MXCSR when any of the related features is in use */ mask = XFEATURE_MASK_FP | XFEATURE_MASK_SSE | XFEATURE_MASK_YMM; if (hdr.xfeatures & mask) { -- 2.17.1
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