From: alex.bennee@linaro•org (Alex Bennée)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v10 06/18] arm64: fpsimd: Generalise context saving for non-task contexts
Date: Thu, 24 May 2018 10:41:40 +0100 [thread overview]
Message-ID: <878t89tmp7.fsf@linaro.org> (raw)
In-Reply-To: <20180524090322.GQ13470@e103592.cambridge.arm.com>
Dave Martin <Dave.Martin@arm•com> writes:
> On Wed, May 23, 2018 at 09:15:11PM +0100, Alex Benn?e wrote:
>>
>> Dave Martin <Dave.Martin@arm•com> writes:
>>
>> > In preparation for allowing non-task (i.e., KVM vcpu) FPSIMD
>> > contexts to be handled by the fpsimd common code, this patch adapts
>> > task_fpsimd_save() to save back the currently loaded context,
>> > removing the explicit dependency on current.
>> >
>> > The relevant storage to write back to in memory is now found by
>> > examining the fpsimd_last_state percpu struct.
>> >
>> > fpsimd_save() does nothing unless TIF_FOREIGN_FPSTATE is clear, and
>> > fpsimd_last_state is updated under local_bh_disable() or
>> > local_irq_disable() everywhere that TIF_FOREIGN_FPSTATE is cleared:
>> > thus, fpsimd_save() will write back to the correct storage for the
>> > loaded context.
>> >
>> > No functional change.
>> >
>> > Signed-off-by: Dave Martin <Dave.Martin@arm•com>
>> > Acked-by: Marc Zyngier <marc.zyngier@arm•com>
>> > Acked-by: Catalin Marinas <catalin.marinas@arm•com>
>> > ---
>> > arch/arm64/kernel/fpsimd.c | 25 +++++++++++++------------
>> > 1 file changed, 13 insertions(+), 12 deletions(-)
>> >
>> > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
>> > index 9d85373..3aa100a 100644
>> > --- a/arch/arm64/kernel/fpsimd.c
>> > +++ b/arch/arm64/kernel/fpsimd.c
>> > @@ -270,13 +270,15 @@ static void task_fpsimd_load(void)
>> > }
>> >
>> > /*
>> > - * Ensure current's FPSIMD/SVE storage in thread_struct is up to date
>> > - * with respect to the CPU registers.
>> > + * Ensure FPSIMD/SVE storage in memory for the loaded context is up to
>> > + * date with respect to the CPU registers.
>> > *
>> > * Softirqs (and preemption) must be disabled.
>> > */
>> > -static void task_fpsimd_save(void)
>> > +static void fpsimd_save(void)
>> > {
>> > + struct user_fpsimd_state *st = __this_cpu_read(fpsimd_last_state.st);
>> > +
>>
>> I thought I was missing something but the only write I saw of this was:
>>
>> __this_cpu_write(fpsimd_last_state.st, NULL);
>>
>> which implied to me it is possible to have an invalid de-reference. I
>> did figure it out eventually as fpsimd_bind_state_to_cpu uses a more
>> indirect this_cpu_ptr idiom for tweaking this. I guess a reference to
>> fpsimd_bind_[task|state]_to_cpu in the comment would have helped my
>> confusion.
>
> How about:
>
> static void fpsimd_save(void)
> {
> struct user_fpsimd_state *st = __this_cpu_read(fpsimd_last_state.st);
> + /* set by fpsimd_bind_to_cpu() */
Great, thanks ;-)
--
Alex Benn?e
next prev parent reply other threads:[~2018-05-24 9:41 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-22 16:05 [PATCH v10 00/18] KVM: arm64: Optimise FPSIMD context switching Dave Martin
2018-05-22 16:05 ` [PATCH v10 01/18] arm64: fpsimd: Fix TIF_FOREIGN_FPSTATE after invalidating cpu regs Dave Martin
2018-05-23 11:33 ` Christoffer Dall
2018-05-23 13:44 ` Alex Bennée
2018-05-23 13:46 ` Catalin Marinas
2018-05-22 16:05 ` [PATCH v10 02/18] thread_info: Add update_thread_flag() helpers Dave Martin
2018-05-23 13:46 ` Alex Bennée
2018-05-23 13:57 ` Dave Martin
2018-05-23 14:35 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 03/18] arm64: Use update{,_tsk}_thread_flag() Dave Martin
2018-05-23 13:48 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 04/18] KVM: arm/arm64: Introduce kvm_arch_vcpu_run_pid_change Dave Martin
2018-05-23 14:34 ` Alex Bennée
2018-05-23 14:40 ` Dave Martin
2018-05-24 8:11 ` Christoffer Dall
2018-05-24 9:18 ` Alex Bennée
2018-05-24 10:04 ` Dave Martin
2018-05-22 16:05 ` [PATCH v10 05/18] KVM: arm64: Convert lazy FPSIMD context switch trap to C Dave Martin
2018-05-23 19:35 ` Alex Bennée
2018-05-24 8:12 ` Christoffer Dall
2018-05-24 8:54 ` Dave Martin
2018-05-24 9:14 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 06/18] arm64: fpsimd: Generalise context saving for non-task contexts Dave Martin
2018-05-23 20:15 ` Alex Bennée
2018-05-24 9:03 ` Dave Martin
2018-05-24 9:41 ` Alex Bennée [this message]
2018-05-22 16:05 ` [PATCH v10 07/18] arm64: fpsimd: Eliminate task->mm checks Dave Martin
2018-05-23 11:48 ` Christoffer Dall
2018-05-23 13:31 ` Dave Martin
2018-05-23 14:56 ` Catalin Marinas
2018-05-23 15:03 ` Dave Martin
2018-05-23 16:42 ` Catalin Marinas
2018-05-24 8:33 ` Christoffer Dall
2018-05-24 9:16 ` Alex Bennée
2018-05-24 9:50 ` Dave Martin
2018-05-24 10:06 ` Christoffer Dall
2018-05-24 14:37 ` Dave Martin
2018-05-25 9:00 ` Christoffer Dall
2018-05-25 9:45 ` Dave Martin
2018-05-25 11:28 ` Christoffer Dall
2018-05-24 9:19 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 08/18] arm64/sve: Refactor user SVE trap maintenance for external use Dave Martin
2018-05-23 20:16 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 09/18] KVM: arm64: Repurpose vcpu_arch.debug_flags for general-purpose flags Dave Martin
2018-05-24 9:21 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 10/18] KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing Dave Martin
2018-05-24 10:09 ` Alex Bennée
2018-05-24 10:18 ` Dave Martin
2018-05-22 16:05 ` [PATCH v10 11/18] arm64/sve: Move read_zcr_features() out of cpufeature.h Dave Martin
2018-05-24 10:12 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 12/18] arm64/sve: Switch sve_pffr() argument from task to thread Dave Martin
2018-05-24 10:12 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 13/18] arm64/sve: Move sve_pffr() to fpsimd.h and make inline Dave Martin
2018-05-24 10:20 ` Alex Bennée
2018-05-24 11:22 ` Dave Martin
2018-05-22 16:05 ` [PATCH v10 14/18] KVM: arm64: Save host SVE context as appropriate Dave Martin
2018-05-23 14:59 ` Catalin Marinas
2018-05-24 9:11 ` Christoffer Dall
2018-05-24 14:49 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 15/18] KVM: arm64: Remove eager host SVE state saving Dave Martin
2018-05-24 14:54 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 16/18] KVM: arm64: Remove redundant *exit_code changes in fpsimd_guest_exit() Dave Martin
2018-05-24 9:11 ` Christoffer Dall
2018-05-24 15:02 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 17/18] KVM: arm64: Fold redundant exit code checks out of fixup_guest_exit() Dave Martin
2018-05-24 9:12 ` Christoffer Dall
2018-05-24 15:06 ` Alex Bennée
2018-05-22 16:05 ` [PATCH v10 18/18] KVM: arm64: Invoke FPSIMD context switch trap from C Dave Martin
2018-05-24 15:09 ` Alex Bennée
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