linux-hardening - Re: [PATCH V2] ACPI: APEI: Use ERST timeout for slow devices

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Date: Tue, 24 Oct 2023 08:24:21 -0700
From: Tony Luck <tony.luck@...el.com>
To: Jeshua Smith <jeshuas@...dia.com>
Cc: keescook@...omium.org, gpiccoli@...lia.com, rafael@...nel.org,
	lenb@...nel.org, james.morse@....com, bp@...en8.de,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org, linux-tegra@...r.kernel.org,
	treding@...dia.com, jonathanh@...dia.com
Subject: Re: [PATCH V2] ACPI: APEI: Use ERST timeout for slow devices

On Wed, Jul 12, 2023 at 10:34:48PM +0000, Jeshua Smith wrote:
> Slow devices such as flash may not meet the default 1ms timeout value,
> so use the ERST max execution time value that they provide as the
> timeout if it is larger.
> 
> Signed-off-by: Jeshua Smith <jeshuas@...dia.com>

> +/* ERST Exec max timings */
> +#define ERST_EXEC_TIMING_MAX_MASK      0xFFFFFFFF00000000
> +#define ERST_EXEC_TIMING_MAX_SHIFT     32

I've recently become a fan of <linux/bitfield.h> I think this would
be easier on the eyes as:

#define ERST_EXEC_TIMING_MAX	GENMASK_ULL(63, 32)

> +static inline u64 erst_get_timeout(void)
> +{
> +	u64 timeout = FIRMWARE_TIMEOUT;
> +
> +	if (erst_erange.attr & ERST_RANGE_SLOW) {
> +		timeout = ((erst_erange.timings & ERST_EXEC_TIMING_MAX_MASK) >>
> +			ERST_EXEC_TIMING_MAX_SHIFT) * NSEC_PER_MSEC;

then this becomes:

		timeout = FIELD_GET(ERST_EXEC_TIMING_MAX, erst_erange.timings) *
			  NSEC_PER_MSEC;

> +		if (timeout < FIRMWARE_TIMEOUT)
> +			timeout = FIRMWARE_TIMEOUT;

But that's just a matter of style.  Otherwise the patch looks fine.

Reviewed-by: Tony Luck <tony.luck@...el.com>

-Tony