linux-kernel - Re: [GIT pull] core/urgent for v5.18-rc6

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Date:   Mon, 9 May 2022 16:02:24 +0100
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Zhangfei Gao <zhangfei.gao@...mail.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [GIT pull] core/urgent for v5.18-rc6

Hi,

On Sun, May 08, 2022 at 11:36:23AM -0700, Linus Torvalds wrote:
> And yes, the mmu notifiers do then take that mmgrab reference to the
> mm, so it all works.
> 
> But it sure looks horrendously ugly. Saving off a 'struct mm_struct'
> pointer with having basically an accidental reference to it is WRONG.

Yes it is fragile. We're currently reworking iommu_sva_bind_device() to
factor more code into the IOMMU core and to add explicit mmgrab/mmdrop, so
once this lands we won't depend on mmu_notifier_register() anymore to hold
the mm reference.

https://lore.kernel.org/linux-iommu/20220502014842.991097-9-baolu.lu@linux.intel.com/

Thanks,
Jean