From: Catalin Marinas <catalin.marinas@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>, Marc Zyngier <maz@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.linux.dev, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 3/8] arm64/fpsimd: Have KVM explicitly say which FP registers to save
Date: Sun, 13 Nov 2022 22:27:03 +0000 [thread overview]
Message-ID: <Y3FvN85aHXrdEIT5@arm.com> (raw)
In-Reply-To: <20221021230321.1159287-4-broonie@kernel.org>
On Sat, Oct 22, 2022 at 12:03:16AM +0100, Mark Brown wrote:
> In order to avoid needlessly saving and restoring the guest registers KVM
> relies on the host FPSMID code to save the guest registers when we context
> switch away from the guest. This is done by binding the KVM guest state to
> the CPU on top of the task state that was originally there, then carefully
> managing the TIF_SVE flag for the task to cause the host to save the full
> SVE state when needed regardless of the needs of the host task. This works
> well enough but isn't terribly direct about what is going on and makes it
> much more complicated to try to optimise what we're doing with the SVE
> register state.
>
> Let's instead have KVM pass in the register state it wants saving when it
> binds to the CPU. We introduce a new FP_STATE_TASK for use during normal
> task binding to indicate that we should base our decisions on the current
> task. This should not ben used when actually saving. Ideally we might
s/ben/be/
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index 3cce0a4c4e8d..1d48398cb6dc 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -123,6 +123,7 @@ enum vec_type {
> };
>
> enum fp_type {
> + FP_STATE_TASK, /* Save based on current task state. */
Nitpick: FP_STATE_CURRENT instead?
Reviewed-by: Catalin Marinas
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next prev parent reply other threads:[~2022-11-13 22:28 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-21 23:03 [PATCH v4 0/8] arm64/sve: Clean up KVM integration and optimise syscalls Mark Brown
2022-10-21 23:03 ` [PATCH v4 1/8] KVM: arm64: Discard any SVE state when entering KVM guests Mark Brown
2022-11-13 22:00 ` Catalin Marinas
2022-10-21 23:03 ` [PATCH v4 2/8] arm64/fpsimd: Track the saved FPSIMD state type separately to TIF_SVE Mark Brown
2022-11-13 22:12 ` Catalin Marinas
2022-11-14 11:10 ` Mark Brown
2022-10-21 23:03 ` [PATCH v4 3/8] arm64/fpsimd: Have KVM explicitly say which FP registers to save Mark Brown
2022-11-13 22:27 ` Catalin Marinas [this message]
2022-10-21 23:03 ` [PATCH v4 4/8] arm64/fpsimd: Stop using TIF_SVE to manage register saving in KVM Mark Brown
2022-11-13 22:30 ` Catalin Marinas
2022-10-21 23:03 ` [PATCH v4 5/8] arm64/fpsimd: Load FP state based on recorded data type Mark Brown
2022-11-14 9:24 ` Catalin Marinas
2022-10-21 23:03 ` [PATCH v4 6/8] arm64/fpsimd: SME no longer requires SVE register state Mark Brown
2022-11-14 10:18 ` Catalin Marinas
2022-10-21 23:03 ` [PATCH v4 7/8] arm64/sve: Leave SVE enabled on syscall if we don't context switch Mark Brown
2022-11-14 10:31 ` Catalin Marinas
2022-11-14 11:25 ` Mark Brown
2022-10-21 23:03 ` [PATCH v4 8/8] arm64/fp: Use a struct to pass data to fpsimd_bind_state_to_cpu() Mark Brown
2022-11-14 10:33 ` Catalin Marinas
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