linux-kernel - Re: [PATCH RFC V3 7/9] x86/entry: Preserve PKRS MSR across exceptions

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Message-ID: <20201015041808.GS2046448@iweiny-DESK2.sc.intel.com>
Date:   Wed, 14 Oct 2020 21:18:08 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V3 7/9] x86/entry: Preserve PKRS MSR across exceptions

On Wed, Oct 14, 2020 at 09:06:44PM -0700, Dave Hansen wrote:
> On 10/14/20 8:46 PM, Ira Weiny wrote:
> > On Tue, Oct 13, 2020 at 11:52:32AM -0700, Dave Hansen wrote:
> >> On 10/9/20 12:42 PM, ira.weiny@...el.com wrote:
> >>> @@ -341,6 +341,9 @@ noinstr void irqentry_enter(struct pt_regs *regs, irqentry_state_t *state)
> >>>  	/* Use the combo lockdep/tracing function */
> >>>  	trace_hardirqs_off();
> >>>  	instrumentation_end();
> >>> +
> >>> +done:
> >>> +	irq_save_pkrs(state);
> >>>  }
> >> One nit: This saves *and* sets PKRS.  It's not obvious from the call
> >> here that PKRS is altered at this site.  Seems like there could be a
> >> better name.
> >>
> >> Even if we did:
> >>
> >> 	irq_save_set_pkrs(state, INIT_VAL);
> >>
> >> It would probably compile down to the same thing, but be *really*
> >> obvious what's going on.
> > I suppose that is true.  But I think it is odd having a parameter which is the
> > same for every call site.
> 
> Well, it depends on what you optimize for.  I'm trying to optimize for
> the code being understood quickly the first time someone reads it.  To
> me, that's more important than minimizing the number of function
> parameters (which are essentially free).
>

Agreed.  Sorry I was not trying to be confrontational.  There is just enough
other things which are going to take me time to get right I need to focus on
them...  :-D

Sorry,
Ira