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Date:   Wed, 9 Nov 2022 18:14:45 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        "H. Peter Anvin" <hpa@zytor.com>, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org,
        syzbot+8cdd16fd5a6c0565e227@syzkaller.appspotmail.com
Subject: Re: [PATCH 3/3] x86/kasan: Populate shadow for shared chunk of the
 CPU entry area
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References: <20221104183247.834988-1-seanjc@google.com>
 <20221104183247.834988-4-seanjc@google.com>
 <06debc96-ea5d-df61-3d2e-0d1d723e55b7@gmail.com>
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On Tue, Nov 08, 2022, Andrey Ryabinin wrote:
> 
> On 11/4/22 21:32, Sean Christopherson wrote:
> > @@ -409,6 +410,15 @@ void __init kasan_init(void)
> >  		kasan_mem_to_shadow((void *)VMALLOC_END + 1),
> >  		(void *)shadow_cea_begin);
> >  
> > +	/*
> > +	 * Populate the shadow for the shared portion of the CPU entry area.
> > +	 * Shadows for the per-CPU areas are mapped on-demand, as each CPU's
> > +	 * area is randomly placed somewhere in the 512GiB range and mapping
> > +	 * the entire 512GiB range is prohibitively expensive.
> > +	 */
> > +	kasan_populate_shadow(shadow_cea_begin,
> > +			      shadow_cea_per_cpu_begin, 0);
> > +
> 
> I think we can extend the kasan_populate_early_shadow() call above up to
> shadow_cea_per_cpu_begin point, instead of this.
> populate_early_shadow() maps single RO zeroed page. No one should write to the shadow for IDT.
> KASAN only needs writable shadow for linear mapping/stacks/vmalloc/global variables.

Any objection to simply converting this to use kasan_populate_early_shadow(),
i.e. to keeping a separate "populate" call for the CPU entry area?  Purely so
that it's more obvious that a small portion of the overall CPU entry area is
mapped during init.