linux-kernel - Re: [PATCH v2 2/4] x86/mm/64: Flush global TLB on AP bringup

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Message-ID: <YVXBNeF8HZwtquE1@8bytes.org>
Date:   Thu, 30 Sep 2021 15:52:53 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Joerg Roedel <jroedel@...e.de>,
        Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brijesh Singh <brijesh.singh@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] x86/mm/64: Flush global TLB on AP bringup

On Wed, Sep 29, 2021 at 08:09:38AM -0700, Dave Hansen wrote:
> On 9/29/21 7:54 AM, Joerg Roedel wrote:
>
> > +	__flush_tlb_all();
> >  }
> 
> Is there a reason to do this flush here as opposed to doing it closer to
> the CR3 write where we switch away from trampoline_pgd?  cr4_init()
> seems like an odd place.

Yeah, the reason is that global flushing is done by toggling CR4.PGE and
I didn't want to do that before CR4 is set up.

The CR3 switch away from the trampoline_pgd for secondary CPUs on x86-64
happens in head_64.S already. I will add some asm to do a global flush
there right after the CR3 switch. Secondary CPUs are already on kernel
virtual addresses at this point.


	Joerg