Messages in this thread Patch in this message | | | From | "Chang S. Bae" <> | Subject | [PATCH v9 08/26] x86/fpu/xstate: Introduce helpers to manage the XSTATE buffer dynamically | Date | Fri, 30 Jul 2021 07:59:39 -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 reserved to be saved in the XSTATE buffer.
alloc_xstate_buffer() uses vzalloc(). If use of this mechanism grows to allocate buffers larger than 64KB, a more sophisticated allocation scheme that includes purpose-built reclaim capability might be justified.
Introduce a new helper -- get_xstate_size() 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 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 | 8 ++ arch/x86/include/asm/fpu/xstate.h | 3 + arch/x86/include/asm/trace/fpu.h | 5 ++ arch/x86/kernel/fpu/core.c | 18 +++-- arch/x86/kernel/fpu/xstate.c | 127 ++++++++++++++++++++++++++++++ 5 files changed, 154 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index c7826708f27f..c0192e16cadb 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -336,6 +336,14 @@ struct fpu { */ unsigned long avx512_timestamp; + /* + * @state_mask: + * + * The bitmap represents state components reserved 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 d722e774a9f9..45735441fbe8 100644 --- a/arch/x86/include/asm/fpu/xstate.h +++ b/arch/x86/include/asm/fpu/xstate.h @@ -146,6 +146,9 @@ extern unsigned int get_xstate_config(enum xstate_config cfg); void set_xstate_config(enum xstate_config cfg, unsigned int value); void *get_xsave_addr(struct fpu *fpu, int xfeature_nr); +unsigned int get_xstate_size(u64 mask); +int alloc_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/include/asm/trace/fpu.h b/arch/x86/include/asm/trace/fpu.h index ef82f4824ce7..b691c2db47c7 100644 --- a/arch/x86/include/asm/trace/fpu.h +++ b/arch/x86/include/asm/trace/fpu.h @@ -89,6 +89,11 @@ DEFINE_EVENT(x86_fpu, x86_fpu_xstate_check_failed, TP_ARGS(fpu) ); +DEFINE_EVENT(x86_fpu, x86_fpu_xstate_alloc_failed, + TP_PROTO(struct fpu *fpu), + TP_ARGS(fpu) +); + #undef TRACE_INCLUDE_PATH #define TRACE_INCLUDE_PATH asm/trace/ #undef TRACE_INCLUDE_FILE diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 6390562516c9..16abc0357e2e 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 = get_xstate_config(XSTATE_MIN_SIZE); + mask = fpu->state_mask; + size = get_xstate_size(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, get_xstate_config(XSTATE_MIN_SIZE)); @@ -380,6 +381,9 @@ 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 (boot_cpu_has(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 5f58dca4c6b7..26f6d5e0f1ed 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_aligns[XFEATURE_MAX] __ro_after_init = + { [ 0 ... XFEATURE_MAX - 1] = false}; /** * struct fpu_xstate_buffer_config - xstate buffer configuration @@ -174,6 +182,55 @@ static bool xfeature_is_supervisor(int xfeature_nr) return ecx & 1; } +/** + * get_xstate_size - Calculate an xstate buffer size + * @mask: This bitmap tells which components reserved 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 get_xstate_size(u64 mask) +{ + unsigned int 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 get_xstate_config(XSTATE_MIN_SIZE); + else if (mask == xfeatures_mask_all) + return get_xstate_config(XSTATE_MAX_SIZE); + + nr = fls64(mask) - 1; + + if (!boot_cpu_has(X86_FEATURE_XSAVES)) + return xstate_offsets[nr] + xstate_sizes[nr]; + + if ((xfeatures_mask_all & (BIT_ULL(nr + 1) - 1)) == mask) + return xstate_comp_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 (size = FXSAVE_SIZE + XSAVE_HDR_SIZE, i = FIRST_EXTENDED_XFEATURE; i <= nr; i++) { + if (!(mask & BIT_ULL(i))) + continue; + + if (xstate_aligns[i]) + size = ALIGN(size, 64); + size += xstate_sizes[i]; + } + return size; +} + /* * Enable the extended processor state save/restore feature. * Called once per CPU onlining. @@ -224,10 +281,12 @@ static void __init setup_xstate_features(void) xstate_offsets[XFEATURE_FP] = 0; xstate_sizes[XFEATURE_FP] = offsetof(struct fxregs_state, xmm_space); + xstate_aligns[XFEATURE_FP] = true; xstate_offsets[XFEATURE_SSE] = xstate_sizes[XFEATURE_FP]; xstate_sizes[XFEATURE_SSE] = sizeof_field(struct fxregs_state, xmm_space); + xstate_aligns[XFEATURE_SSE] = true; for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) { if (!xfeature_enabled(i)) @@ -245,6 +304,7 @@ static void __init setup_xstate_features(void) continue; xstate_offsets[i] = ebx; + xstate_aligns[i] = (ecx & 2) ? true : false; /* * In our xstate size checks, we assume that the highest-numbered @@ -848,6 +908,9 @@ void __init fpu__init_system_xstate(void) if (err) goto out_disable; + /* Make sure init_task does not include the dynamic user 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: @@ -1038,6 +1101,70 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, } #endif /* ! CONFIG_ARCH_HAS_PKEYS */ +void free_xstate_buffer(struct fpu *fpu) +{ + /* Free up only the dynamically-allocated memory. */ + if (fpu->state != &fpu->__default_state) + vfree(fpu->state); +} + +/** + * alloc_xstate_buffer - Allocate 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. + * + * Use vmalloc() simply here. If the task with a vmalloc()-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 alloc_xstate_buffer(struct fpu *fpu, u64 mask) +{ + union fpregs_state *state; + unsigned int oldsz, newsz; + u64 state_mask; + + state_mask = fpu->state_mask | mask; + + oldsz = get_xstate_size(fpu->state_mask); + newsz = get_xstate_size(state_mask); + + if (oldsz >= newsz) + return 0; + + state = vzalloc(newsz); + if (!state) { + /* + * When allocation requested from #NM, the error code may + * not be populated well. Then, this tracepoint is useful + * for providing the failure context. + */ + trace_x86_fpu_xstate_alloc_failed(fpu); + return -ENOMEM; + } + + if (boot_cpu_has(X86_FEATURE_XSAVES)) + fpstate_init_xstate(&state->xsave, state_mask); + + /* + * As long as the register state is intact, save the xstate in the + * new buffer at the next context copy/switch or potentially + * ptrace-driven xstate writing. + */ + + 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) { -- 2.17.1
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