Messages in this thread Patch in this message | | | From | "Chang S. Bae" <> | Subject | [PATCH v3 07/21] x86/fpu/xstate: Introduce helpers to manage dynamic xstate buffers | Date | Wed, 23 Dec 2020 07:57:03 -0800 |
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The static per-task xstate buffer contains the extended register states -- but it is not expandable at runtime. Introduce runtime methods and new fpu struct fields to support the expansion.
fpu->state_mask indicates the saved states per task and fpu->state_ptr points to the dynamically allocated buffer.
alloc_xstate_buffer() uses vmalloc(). 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.
No functional change until the kernel supports dynamic user states.
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 v2: * Updated the changelog with task->fpu removed. (Boris 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 | 29 ++++++-- arch/x86/include/asm/fpu/xstate.h | 3 + arch/x86/include/asm/trace/fpu.h | 5 ++ arch/x86/kernel/fpu/core.c | 3 + arch/x86/kernel/fpu/xstate.c | 115 ++++++++++++++++++++++++++++++ 5 files changed, 150 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index f5a38a5f3ae1..3fc6dbbe3ede 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -336,14 +336,33 @@ struct fpu { */ unsigned long avx512_timestamp; + /* + * @state_mask: + * + * The state component bitmap. It indicates the saved xstate in + * either @state or @state_ptr. The map value starts to be aligned + * with @state and then with @state_ptr once it is in use. + */ + u64 state_mask; + + /* + * @state_ptr: + * + * Copy of all extended register states, in a dynamically allocated + * buffer. When a task is using extended features, the register state + * is always the most current. This state copy is more recent than + * @state. If the task context-switches away, they get saved here, + * representing the xstate. + */ + union fpregs_state *state_ptr; + /* * @state: * - * In-memory copy of all FPU registers that we save/restore - * over context switches. If the task is using the FPU then - * the registers in the FPU are more recent than this state - * copy. If the task context-switches away then they get - * saved here and represent the FPU state. + * Copy of some extended register state. If a task uses a dynamically + * allocated buffer, @state_ptr, then it has a more recent state copy + * than this. This copy follows the same attributes as described for + * @state_ptr. */ union fpregs_state state; /* diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h index 6ce8350672c2..379e8f8b8440 100644 --- a/arch/x86/include/asm/fpu/xstate.h +++ b/arch/x86/include/asm/fpu/xstate.h @@ -103,6 +103,9 @@ extern void __init update_regset_xstate_info(unsigned int size, u64 xstate_mask); void *get_xsave_addr(struct fpu *fpu, int xfeature_nr); +int alloc_xstate_buffer(struct fpu *fpu, u64 mask); +void free_xstate_buffer(struct fpu *fpu); + const void *get_xsave_field_ptr(int xfeature_nr); int using_compacted_format(void); int xfeature_size(int xfeature_nr); diff --git a/arch/x86/include/asm/trace/fpu.h b/arch/x86/include/asm/trace/fpu.h index 879b77792f94..bf88b3333873 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 1a428803e6b2..6dafed34be4f 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -235,6 +235,9 @@ int fpu__copy(struct task_struct *dst, struct task_struct *src) */ memset(&dst_fpu->state.xsave, 0, fpu_kernel_xstate_min_size); + dst_fpu->state_mask = xfeatures_mask_all & ~xfeatures_mask_user_dynamic; + dst_fpu->state_ptr = NULL; + /* * If the FPU registers are not current just memcpy() the state. * Otherwise save current FPU registers directly into the child's FPU diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 2012b17b1793..af4d7d9aa977 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 @@ -71,6 +73,7 @@ static unsigned int xstate_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = static unsigned int xstate_sizes[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1}; static unsigned int xstate_comp_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1}; static unsigned int xstate_supervisor_only_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1}; +static bool xstate_aligns[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = false}; /* * The XSAVE area of kernel can be in standard or compacted format; @@ -130,6 +133,48 @@ static bool xfeature_is_supervisor(int xfeature_nr) return ecx & 1; } +/* + * Available once those arrays for the offset, size, and alignment info are set up, + * by setup_xstate_features(). + */ +static unsigned int get_xstate_size(u64 mask) +{ + unsigned int size; + u64 xmask; + int i, nr; + + if (!mask) + return 0; + else if (mask == (xfeatures_mask_all & ~xfeatures_mask_user_dynamic)) + return fpu_kernel_xstate_min_size; + else if (mask == xfeatures_mask_all) + return fpu_kernel_xstate_max_size; + + nr = fls64(mask) - 1; + + if (!using_compacted_format()) + return xstate_offsets[nr] + xstate_sizes[nr]; + + xmask = BIT_ULL(nr + 1) - 1; + + if (mask == (xmask & xfeatures_mask_all)) + return xstate_comp_offsets[nr] + xstate_sizes[nr]; + + /* + * Calculate the size by summing up each state together, since no known + * size found with the xstate buffer format out of the given mask. + */ + 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; +} + /* * When executing XSAVEOPT (or other optimized XSAVE instructions), if * a processor implementation detects that an FPU state component is still @@ -270,10 +315,12 @@ 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)) @@ -291,6 +338,7 @@ 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 @@ -755,6 +803,9 @@ static bool is_supported_xstate_size(unsigned int test_xstate_size) return false; } +/* The watched threshold size of dynamically allocated xstate buffer */ +#define XSTATE_BUFFER_MAX_BYTES (64 * 1024) + static int __init init_xstate_size(void) { /* Recompute the context size for enabled features: */ @@ -779,6 +830,14 @@ static int __init init_xstate_size(void) if (!is_supported_xstate_size(fpu_kernel_xstate_min_size)) return -EINVAL; + /* + * When allocating buffers larger than the threshold, a more sophisticated + * mechanism might be considerable. + */ + if (fpu_kernel_xstate_max_size > XSTATE_BUFFER_MAX_BYTES) + pr_warn("x86/fpu: xstate buffer too large (%u > %u)\n", + fpu_kernel_xstate_max_size, XSTATE_BUFFER_MAX_BYTES); + /* * User space is always in standard format. */ @@ -869,6 +928,9 @@ 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: @@ -1089,6 +1151,59 @@ static inline bool xfeatures_mxcsr_quirk(u64 xfeatures) return true; } +void free_xstate_buffer(struct fpu *fpu) +{ + vfree(fpu->state_ptr); +} + +/* + * Allocate an xstate buffer with the size calculated based on 'mask'. + * + * The allocation mechanism does not shrink or reclaim the buffer. + */ +int alloc_xstate_buffer(struct fpu *fpu, u64 mask) +{ + union fpregs_state *state_ptr; + 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; + + if (newsz > fpu_kernel_xstate_max_size) { + pr_warn_once("x86/fpu: xstate buffer too large (%u > %u bytes)\n", + newsz, fpu_kernel_xstate_max_size); + XSTATE_WARN_ON(1); + return 0; + } + + /* We need 64B aligned pointer, but vmalloc() returns a page-aligned address. */ + state_ptr = vmalloc(newsz); + if (!state_ptr) { + trace_x86_fpu_xstate_alloc_failed(fpu); + return -ENOMEM; + } + + memset(state_ptr, 0, newsz); + if (using_compacted_format()) + fpstate_init_xstate(&state_ptr->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. + */ + + vfree(fpu->state_ptr); + fpu->state_ptr = state_ptr; + fpu->state_mask = state_mask; + return 0; +} + static void fill_gap(struct membuf *to, unsigned *last, unsigned offset) { if (*last >= offset) -- 2.17.1
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