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x86/fpu: Remove fpu->initialized

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The struct fpu.initialized member is always set to one for user tasks
and zero for kernel tasks. This avoids saving/restoring the FPU
registers for kernel threads.

The ->initialized = 0 case for user tasks has been removed in previous
changes, for instance, by doing an explicit unconditional init at fork()
time for FPU-less systems which was otherwise delayed until the emulated
opcode.

The context switch code (switch_fpu_prepare() + switch_fpu_finish())
can't unconditionally save/restore registers for kernel threads. Not
only would it slow down the switch but also load a zeroed xcomp_bv for
XSAVES.

For kernel_fpu_begin() (+end) the situation is similar: EFI with runtime
services uses this before alternatives_patched is true. Which means that
this function is used too early and it wasn't the case before.

For those two cases, use current->mm to distinguish between user and
kernel thread. For kernel_fpu_begin() skip save/restore of the FPU
registers.

During the context switch into a kernel thread don't do anything. There
is no reason to save the FPU state of a kernel thread.

The reordering in __switch_to() is important because the current()
pointer needs to be valid before switch_fpu_finish() is invoked so ->mm
is seen of the new task instead the old one.

N.B.: fpu__save() doesn't need to check ->mm because it is called by
user tasks only.

 [ bp: Massage. ]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Aubrey Li <aubrey.li@intel.com>
Cc: Babu Moger <Babu.Moger@amd.com>
Cc: "Chang S. Bae" <chang.seok.bae@intel.com>
Cc: Dmitry Safonov <dima@arista.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Nicolai Stange <nstange@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-8-bigeasy@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior
2019-04-03 18:41:36 +02:00
committed by Borislav Petkov
parent 39388e80f9
commit 2722146eb7
12 changed files with 53 additions and 121 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
arch/x86/include/asm/fpu/internal.h
View File

@@ -494,11 +494,14 @@ static inline void fpregs_activate(struct fpu *fpu)
*
* - switch_fpu_finish() restores the new state as
* necessary.
*
* The FPU context is only stored/restored for a user task and
* ->mm is used to distinguish between kernel and user threads.
*/
static inline void
switch_fpu_prepare(struct fpu *old_fpu, int cpu)
{
if (static_cpu_has(X86_FEATURE_FPU) && old_fpu->initialized) {
if (static_cpu_has(X86_FEATURE_FPU) && current->mm) {
if (!copy_fpregs_to_fpstate(old_fpu))
old_fpu->last_cpu = -1;
else
@@ -506,8 +509,7 @@ switch_fpu_prepare(struct fpu *old_fpu, int cpu)
/* But leave fpu_fpregs_owner_ctx! */
trace_x86_fpu_regs_deactivated(old_fpu);
} else
old_fpu->last_cpu = -1;
}
}
/*
@@ -520,12 +522,12 @@ switch_fpu_prepare(struct fpu *old_fpu, int cpu)
*/
static inline void switch_fpu_finish(struct fpu *new_fpu, int cpu)
{
bool preload = static_cpu_has(X86_FEATURE_FPU) &&
new_fpu->initialized;
if (static_cpu_has(X86_FEATURE_FPU)) {
if (!fpregs_state_valid(new_fpu, cpu)) {
if (current->mm)
copy_kernel_to_fpregs(&new_fpu->state);
}
if (preload) {
if (!fpregs_state_valid(new_fpu, cpu))
copy_kernel_to_fpregs(&new_fpu->state);
fpregs_activate(new_fpu);
}
}

9
arch/x86/include/asm/fpu/types.h
View File

@@ -293,15 +293,6 @@ struct fpu {
*/
unsigned int last_cpu;
/*
* @initialized:
*
* This flag indicates whether this context is initialized: if the task
* is not running then we can restore from this context, if the task
* is running then we should save into this context.
*/
unsigned char initialized;
/*
* @avx512_timestamp:
*

5
arch/x86/include/asm/trace/fpu.h
View File

@@ -13,22 +13,19 @@ DECLARE_EVENT_CLASS(x86_fpu,
TP_STRUCT__entry(
__field(struct fpu *, fpu)
__field(bool, initialized)
__field(u64, xfeatures)
__field(u64, xcomp_bv)
),
TP_fast_assign(
__entry->fpu = fpu;
__entry->initialized = fpu->initialized;
if (boot_cpu_has(X86_FEATURE_OSXSAVE)) {
__entry->xfeatures = fpu->state.xsave.header.xfeatures;
__entry->xcomp_bv = fpu->state.xsave.header.xcomp_bv;
}
),
TP_printk("x86/fpu: %p initialized: %d xfeatures: %llx xcomp_bv: %llx",
TP_printk("x86/fpu: %p xfeatures: %llx xcomp_bv: %llx",
__entry->fpu,
__entry->initialized,
__entry->xfeatures,
__entry->xcomp_bv
)