linux-kernel - Re: [PATCH V7 07/18] x86/pks: Preserve the PKRS MSR on context switch

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Date:   Thu, 25 Nov 2021 16:25:32 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     ira.weiny@...el.com, Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev,
        linux-mm@...ck.org
Subject: Re: [PATCH V7 07/18] x86/pks: Preserve the PKRS MSR on context switch

On Tue, Aug 03 2021 at 21:32, ira weiny wrote:
> @@ -658,6 +659,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
>  	/* Load the Intel cache allocation PQR MSR. */
>  	resctrl_sched_in();
>  
> +	pkrs_write_current();

This is invoked from switch_to() and does this extra get/put_cpu_ptr()
dance in the write function for no reason. Can you please stop sticking
overhead into the hotpath just because?

Thanks,

        tglx