linux-kernel - Re: [PATCH] x86/mm/32: Bring back vmalloc faulting on x86

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Message-ID: <20200903151739.GA28508@8bytes.org>
Date:   Thu, 3 Sep 2020 17:17:39 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <jroedel@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] x86/mm/32: Bring back vmalloc faulting on x86_32

Hi Andy,

On Thu, Sep 03, 2020 at 07:52:35AM -0700, Andy Lutomirski wrote:
> Does this mean we can get rid of arch_sync_kernel_mappings()?  Or
> should we consider adding some locking to make it non-racy again?

Well, removing arch_sync_kernel_mappings() would mean to re-introduce
vmalloc_sync_all() calls all over the place, I am not in favour for
that.

I also thought about locking, but that is not easily doable without
destroying performance/scalability of the vmalloc alloc/free path for
other architectures too. It _could_ be done, but the effort is large and
touches a lot of generic page-table allocation code just for x86-32.
This seemed not worth it while thinking about it.

Regards,

	Joerg