linux-kernel - Re: [PATCH] ACPI: CPPC: Fix bit_offset shift in MASK

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Message-ID: <cc48b26a-f67e-43bc-a29f-2e9f36cecc45@linux.microsoft.com>
Date: Tue, 16 Apr 2024 10:24:27 -0700
From: Jarred White <jarredwhite@...ux.microsoft.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Easwar Hariharan <eahariha@...ux.microsoft.com>,
 "open list:ACPI" <linux-acpi@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>
Cc: Vanshidhar Konda <vanshikonda@...amperecomputing.com>,
 stable@...r.kernel.org
Subject: Re: [PATCH] ACPI: CPPC: Fix bit_offset shift in MASK_VAL macro

On 4/8/2024 10:23 PM, Jarred White wrote:
> Commit 2f4a4d63a193 ("ACPI: CPPC: Use access_width over bit_width for
> system memory accesses") neglected to properly wrap the bit_offset shift
> when it comes to applying the mask. This may cause incorrect values to be
> read and may cause the cpufreq module not be loaded.
> 
> [   11.059751] cpu_capacity: CPU0 missing/invalid highest performance.
> [   11.066005] cpu_capacity: partial information: fallback to 1024 for all CPUs
> 
> Also, corrected the bitmask generation in GENMASK (extra bit being added).
> 
> Fixes: 2f4a4d63a193 ("ACPI: CPPC: Use access_width over bit_width for system memory accesses")
> Signed-off-by: Jarred White <jarredwhite@...ux.microsoft.com>
> CC: Vanshidhar Konda <vanshikonda@...amperecomputing.com>
> CC: stable@...r.kernel.org #5.15+
> ---
>   drivers/acpi/cppc_acpi.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 4bfbe55553f4..00a30ca35e78 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -170,8 +170,8 @@ show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, wraparound_time);
>   #define GET_BIT_WIDTH(reg) ((reg)->access_width ? (8 << ((reg)->access_width - 1)) : (reg)->bit_width)
>   
>   /* Shift and apply the mask for CPC reads/writes */
> -#define MASK_VAL(reg, val) ((val) >> ((reg)->bit_offset & 			\
> -					GENMASK(((reg)->bit_width), 0)))
> +#define MASK_VAL(reg, val) (((val) >> (reg)->bit_offset) & 			\
> +					GENMASK(((reg)->bit_width) - 1, 0))
>   
>   static ssize_t show_feedback_ctrs(struct kobject *kobj,
>   		struct kobj_attribute *attr, char *buf)

Hi Vanshi,

Could you review please?


Thanks,
Jarred