linux-kernel - Re: [PATCH] x86/resctrl: Fix unused variable warning in cache_alloc_hsw

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Message-ID: <d47235e0-7ecd-483e-82c3-78f13c77df67@amd.com>
Date:   Wed, 1 Nov 2023 15:26:23 -0500
From:   "Moger, Babu" <babu.moger@....com>
To:     Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Peter Newman <peternewman@...gle.com>, x86@...nel.org
Cc:     Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH] x86/resctrl: Fix unused variable warning in
 cache_alloc_hsw_probe()

Hi Tony,

On 10/31/23 17:05, Tony Luck wrote:
> In a "W=1" build gcc throws a warning:
> 
> arch/x86/kernel/cpu/resctrl/core.c: In function ‘cache_alloc_hsw_probe’:
> arch/x86/kernel/cpu/resctrl/core.c:139:16: warning: variable ‘h’ set but not used
> 
> Fix by switching from rdmsr() to rdmsrl() using a single u64 argument
> for the MSR value instead of the pair of u32 for the high and low
> halves.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
> This has been annoying me for a while as the only warning from the
> resctrl code when building with W=1.
> 
> N.B. compile tested only. I don't have a Haswell system to check this works.
> 
>  arch/x86/kernel/cpu/resctrl/core.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 19e0681f0435..4084131d391d 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -136,15 +136,16 @@ static inline void cache_alloc_hsw_probe(void)
>  {
>  	struct rdt_hw_resource *hw_res = &rdt_resources_all[RDT_RESOURCE_L3];
>  	struct rdt_resource *r  = &hw_res->r_resctrl;
> -	u32 l, h, max_cbm = BIT_MASK(20) - 1;
> +	u32 max_cbm = BIT_MASK(20) - 1;
> +	u64 l3_cbm_0;
>  
>  	if (wrmsr_safe(MSR_IA32_L3_CBM_BASE, max_cbm, 0))
>  		return;
>  
> -	rdmsr(MSR_IA32_L3_CBM_BASE, l, h);
> +	rdmsrl(MSR_IA32_L3_CBM_BASE, l3_cbm_0);

You are writing 32 bit and reading 64 bit. Why don't you change both to 64
bit?

>  
>  	/* If all the bits were set in MSR, return success */
> -	if (l != max_cbm)
> +	if (l3_cbm_0 != max_cbm)
>  		return;
>  
>  	hw_res->num_closid = 4;

-- 
Thanks
Babu Moger