Re: [PATCH 08/11] arm64: ptrace: prepare for EL1 irq/rcu tracking

From: Will Deacon <will@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: elver@google.com, paulmck@kernel.org, peterz@infradead.org,
	catalin.marinas@arm.com, james.morse@arm.com,
	linux-arm-kernel@lists.infradead.org, dvyukov@google.com
Subject: Re: [PATCH 08/11] arm64: ptrace: prepare for EL1 irq/rcu tracking
Date: Mon, 30 Nov 2020 11:01:47 +0000	[thread overview]
Message-ID: <20201130110146.GC24098@willie-the-truck> (raw)
In-Reply-To: <20201126123602.23454-9-mark.rutland@arm.com>

On Thu, Nov 26, 2020 at 12:35:59PM +0000, Mark Rutland wrote:
> Exceptions from EL1 may be taken when RCU isn't watching (e.g. in idle
> sequences), or when the lockdep hardirqs transiently out-of-sync with
> the hardware state (e.g. in the middle of local_irq_enable()). To
> correctly handle these cases, we'll need to save/restore this state
> across some exceptions taken from EL1.
> 
> A series of subsequent patches will update EL1 exception handlers to
> handle this. In preparation for this, and to avoid dependencies between
> those patches, this patch adds two new fields to struct pt_regs so that
> exception handlers can track this state.
> 
> Note that this is placed in pt_regs as some entry/exit sequences such as
> el1_irq are invoked from assembly, which makes it very difficult to add
> a separate structure as with the irqentry_state used by x86. We can
> separate this once more of the exception logic is moved to C. While the
> fields only need to be bool, they are both made u64 to keep pt_regs
> 16-bite aligned.

"bite" ?!

> There should be no functional change as a result of this patch.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Will Deacon <will@kernel.org>
> ---
>  arch/arm64/include/asm/ptrace.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index 997cf8c8cd52..b4a841d9511d 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -193,6 +193,13 @@ struct pt_regs {
>  	/* Only valid when ARM64_HAS_IRQ_PRIO_MASKING is enabled. */
>  	u64 pmr_save;
>  	u64 stackframe[2];
> +
> +	/*
> +	 * Only valid for some EL1 exceptions.
> +	 * TODO: move this out of pt_regs.

Please drop the "TODO".

Will

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