From: Marc Zyngier <maz@kernel.org> To: Mark Brown <broonie@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com>, Zhang Lei <zhang.lei@jp.fujitsu.com>, Andre Przywara <andre.przywara@arm.com>, Will Deacon <will@kernel.org>, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 2/7] arm64/fpsimd: Track the saved FPSIMD state type separately to TIF_SVE Date: Mon, 11 Jul 2022 15:33:51 +0100 [thread overview] Message-ID: <87h73nlnw0.wl-maz@kernel.org> (raw) In-Reply-To: <YswMB2v9TqPJHDM1@sirena.org.uk> On Mon, 11 Jul 2022 12:39:51 +0100, Mark Brown <broonie@kernel.org> wrote: > > [1 <text/plain; us-ascii (7bit)>] > On Mon, Jul 11, 2022 at 10:40:50AM +0100, Marc Zyngier wrote: > > Mark Brown <broonie@kernel.org> wrote: > > > > + enum fp_state *type; > > > For consistency: s/type/fp_type/ ? > > Sure if nobody else wants a different bikeshed. It really needs a > longer name like fp_state_t or something but that had it's own problems > with non-idiomaticness. I'm not talking about the name of the type, but about the name of the member in the struct fpsimd_last_state_struct. I'd like it to be homogeneous to the name you use in struct kvm_vcpu_arch. 'type' is way too vague a name, and maybe it should be fp_reg_type, as that's what it actually indicates. > > > > if (test_and_clear_tsk_thread_flag(task, TIF_SVE) || > > > - thread_sm_enabled(&task->thread)) > > > + thread_sm_enabled(&task->thread)) { > > > sve_to_fpsimd(task); > > > + task->thread.fp_type = FP_STATE_FPSIMD; > > > Can you move this assignment into the sve_to_fpsimd() helper? > > There are cases where we want a FPSIMD version of the state for > reading but don't want to affect the actual state of the process > (eg, if someone reads the FPSIMD registers via ptrace) so we don't > want to change the active register state just because we converted > it. Adding another API that does the convert and update didn't feel > like it was helping since you then have to remember which API does > what and we already have lots of similarly named functions for > slightly different contexts. I still think the state conversion should be self contained. Sprinkling this context tracking is bound to end-up with a bug, while documenting what is to be used when, or with a helper named explicitly enough ("extract_fp_from_sve()" springs to mind) for ptrace. > > > } else { > > > fpsimd_to_sve(current); > > > + current->thread.fp_type = FP_STATE_SVE; > > > Same thing here. > > There's not the same issue with reading FPSIMD state via the SVE APIs > but for consistency it seems best to always leave these updates in the > callers. I disagree again. I really want these things to be self-contained, and be able to reason about what they do from their name and the arguments they take (and even some documentation). Relying on some extra updates adds complexity to a difficult part of the kernel, and an even more difficult part of the architecture. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org> To: Mark Brown <broonie@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Zhang Lei <zhang.lei@jp.fujitsu.com>, James Morse <james.morse@arm.com>, Alexandru Elisei <alexandru.elisei@arm.com>, Andre Przywara <andre.przywara@arm.com>, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 2/7] arm64/fpsimd: Track the saved FPSIMD state type separately to TIF_SVE Date: Mon, 11 Jul 2022 15:33:51 +0100 [thread overview] Message-ID: <87h73nlnw0.wl-maz@kernel.org> (raw) In-Reply-To: <YswMB2v9TqPJHDM1@sirena.org.uk> On Mon, 11 Jul 2022 12:39:51 +0100, Mark Brown <broonie@kernel.org> wrote: > > [1 <text/plain; us-ascii (7bit)>] > On Mon, Jul 11, 2022 at 10:40:50AM +0100, Marc Zyngier wrote: > > Mark Brown <broonie@kernel.org> wrote: > > > > + enum fp_state *type; > > > For consistency: s/type/fp_type/ ? > > Sure if nobody else wants a different bikeshed. It really needs a > longer name like fp_state_t or something but that had it's own problems > with non-idiomaticness. I'm not talking about the name of the type, but about the name of the member in the struct fpsimd_last_state_struct. I'd like it to be homogeneous to the name you use in struct kvm_vcpu_arch. 'type' is way too vague a name, and maybe it should be fp_reg_type, as that's what it actually indicates. > > > > if (test_and_clear_tsk_thread_flag(task, TIF_SVE) || > > > - thread_sm_enabled(&task->thread)) > > > + thread_sm_enabled(&task->thread)) { > > > sve_to_fpsimd(task); > > > + task->thread.fp_type = FP_STATE_FPSIMD; > > > Can you move this assignment into the sve_to_fpsimd() helper? > > There are cases where we want a FPSIMD version of the state for > reading but don't want to affect the actual state of the process > (eg, if someone reads the FPSIMD registers via ptrace) so we don't > want to change the active register state just because we converted > it. Adding another API that does the convert and update didn't feel > like it was helping since you then have to remember which API does > what and we already have lots of similarly named functions for > slightly different contexts. I still think the state conversion should be self contained. Sprinkling this context tracking is bound to end-up with a bug, while documenting what is to be used when, or with a helper named explicitly enough ("extract_fp_from_sve()" springs to mind) for ptrace. > > > } else { > > > fpsimd_to_sve(current); > > > + current->thread.fp_type = FP_STATE_SVE; > > > Same thing here. > > There's not the same issue with reading FPSIMD state via the SVE APIs > but for consistency it seems best to always leave these updates in the > callers. I disagree again. I really want these things to be self-contained, and be able to reason about what they do from their name and the arguments they take (and even some documentation). Relying on some extra updates adds complexity to a difficult part of the kernel, and an even more difficult part of the architecture. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2022-07-11 14:34 UTC|newest] Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-06-20 12:41 [PATCH v2 0/7] arm64/sve: Clean up KVM integration and optimise syscalls Mark Brown 2022-06-20 12:41 ` Mark Brown 2022-06-20 12:41 ` [PATCH v2 1/7] KVM: arm64: Discard any SVE state when entering KVM guests Mark Brown 2022-06-20 12:41 ` Mark Brown 2022-06-20 12:41 ` [PATCH v2 2/7] arm64/fpsimd: Track the saved FPSIMD state type separately to TIF_SVE Mark Brown 2022-06-20 12:41 ` Mark Brown 2022-07-11 9:40 ` Marc Zyngier 2022-07-11 9:40 ` Marc Zyngier 2022-07-11 11:39 ` Mark Brown 2022-07-11 11:39 ` Mark Brown 2022-07-11 14:33 ` Marc Zyngier [this message] 2022-07-11 14:33 ` Marc Zyngier 2022-07-11 15:53 ` Mark Brown 2022-07-11 15:53 ` Mark Brown 2022-07-20 9:40 ` Marc Zyngier 2022-07-20 9:40 ` Marc Zyngier 2022-07-20 13:51 ` Mark Brown 2022-07-20 13:51 ` Mark Brown 2022-06-20 12:41 ` [PATCH v2 3/7] arm64/fpsimd: Have KVM explicitly say which FP registers to save Mark Brown 2022-06-20 12:41 ` Mark Brown 2022-06-20 12:41 ` [PATCH v2 4/7] arm64/fpsimd: Stop using TIF_SVE to manage register saving in KVM Mark Brown 2022-06-20 12:41 ` Mark Brown 2022-06-20 12:41 ` [PATCH v2 5/7] arm64/fpsimd: Load FP state based on recorded data type Mark Brown 2022-06-20 12:41 ` Mark Brown 2022-06-20 12:41 ` [PATCH v2 6/7] arm64/sve: Leave SVE enabled on syscall if we don't context switch Mark Brown 2022-06-20 12:41 ` Mark Brown 2022-06-20 12:41 ` [PATCH v2 7/7] arm64/sve: Don't zero non-FPSIMD register state on syscall by default Mark Brown 2022-06-20 12:41 ` Mark Brown 2022-07-19 17:35 ` Catalin Marinas 2022-07-19 17:35 ` Catalin Marinas 2022-07-19 19:35 ` Mark Brown 2022-07-19 19:35 ` Mark Brown 2022-07-20 9:20 ` Will Deacon 2022-07-20 9:20 ` Will Deacon 2022-07-20 12:32 ` Mark Brown 2022-07-20 12:32 ` Mark Brown 2022-07-20 9:29 ` Marc Zyngier 2022-07-20 9:29 ` Marc Zyngier 2022-07-20 14:31 ` Mark Brown 2022-07-20 14:31 ` Mark Brown
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