On Thu, Oct 1, 2020 at 1:42 PM Chang S. Bae <[email protected]> wrote: > > task->fpu has a buffer to keep 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 the dynamically allocated area. > > alloc_xstate_area() uses vmalloc() for its scalability. However, set a > threshold (64KB) to watch out a potential need for an alternative > mechanism. > > Also, introduce a new helper -- get_xstate_size() to calculate the area > size. > > No functional change until the kernel supports dynamic user states. > > Signed-off-by: Chang S. Bae <[email protected]> > Reviewed-by: Len Brown <[email protected]> > Cc: [email protected] > Cc: [email protected] > --- > arch/x86/include/asm/fpu/types.h | 29 +++++-- > arch/x86/include/asm/fpu/xstate.h | 3 + > arch/x86/kernel/fpu/core.c | 3 + > arch/x86/kernel/fpu/xstate.c | 124 ++++++++++++++++++++++++++++++ > 4 files changed, 154 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/include/asm/fpu/types.h > b/arch/x86/include/asm/fpu/types.h > index c87364ea6446..4b7756644824 100644 > --- a/arch/x86/include/asm/fpu/types.h > +++ b/arch/x86/include/asm/fpu/types.h > @@ -327,14 +327,33 @@ 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 > + * area, we save and restore over context switches. 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 that we save and restore > + * over context switches. If a task uses a dynamically-allocated > + * area, @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 9aad91c0725b..37728bfcb71e 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_area(struct fpu *fpu, u64 mask, unsigned int *alloc_size); > +void free_xstate_area(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/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c > index 875620fdfe61..e25f7866800e 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_default_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 6e0d8a9699ed..af60332aafef 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> > @@ -69,6 +70,7 @@ 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; > @@ -128,6 +130,48 @@ 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_default_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 area 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 > @@ -268,10 +312,12 @@ 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)) > @@ -289,6 +335,7 @@ 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 > @@ -753,6 +800,9 @@ static bool is_supported_xstate_size(unsigned int > test_xstate_size) > return false; > } > > +/* The watched threshold size of dynamically allocated xstate area */ > +#define XSTATE_AREA_MAX_BYTES (64 * 1024) > + > static int __init init_xstate_size(void) > { > /* Recompute the context size for enabled features: */ > @@ -777,6 +827,14 @@ static int __init init_xstate_size(void) > if (!is_supported_xstate_size(fpu_kernel_xstate_default_size)) > return -EINVAL; > > + /* > + * When observing the allocation goes beyond the threshold, it is > better to consider > + * switching a better scalable mechanism than the current. > + */ > + if (fpu_kernel_xstate_max_size > XSTATE_AREA_MAX_BYTES) > + pr_warn("x86/fpu: xstate buffer too large (%u > %u)\n", > + fpu_kernel_xstate_max_size, XSTATE_AREA_MAX_BYTES); > + > /* > * User space is always in standard format. > */ > @@ -867,6 +925,12 @@ void __init fpu__init_system_xstate(void) > if (err) > goto out_disable; > > + /* > + * At this point, it passed the size sanity check. Have the init_task > take > + * the feature mask. > + */ > + 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: > @@ -1086,6 +1150,66 @@ static inline bool xfeatures_mxcsr_quirk(u64 xfeatures) > return true; > } > > +void free_xstate_area(struct fpu *fpu) > +{ > + vfree(fpu->state_ptr); > +} > + > +/* > + * Allocate a new xstate area with a calculated size, based on the given bit > value. > + * > + * No mechanism implemented yet to shrink or reclaim the xstate area on the > fly, > + * the need of which is subject to the real usage. > + */ > +int alloc_xstate_area(struct fpu *fpu, u64 mask, unsigned int *alloc_size) > +{ > + 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: state buffer too large (%u > %u > bytes)\n", > + newsz, fpu_kernel_xstate_max_size); > + XSTATE_WARN_ON(1); > + return 0; > + } > + > + /* > + * The caller may be under interrupt disabled condition. Ensure > interrupt > + * allowance before the memory allocation, which may involve with > page faults. > + */ > + local_irq_enable(); > + /* We need 64B aligned pointer, but vmalloc() returns a page-aligned > address */ > + state_ptr = vmalloc(newsz);
I'm speechless. First, you can't just enable IRQs here. If IRQs are off, they're off for a reason. Secondly, if they're *on*, you just forgot that fact. And allocating this state from vmalloc() seems questionable. Why are you doing this?
