From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Jarkko Sakkinen" <jarkko.sakkinen@iki.fi>,
"Huang, Kai" <kai.huang@intel.com>, <linux-sgx@vger.kernel.org>,
<linux-mm@kvack.org>
Subject: Re: VMA merging updateds?
Date: Thu, 26 Sep 2024 04:48:56 +0300 [thread overview]
Message-ID: <D4FU6N3RZ30A.2TY1PVOBZ6K8X@kernel.org> (raw)
In-Reply-To: <D4FU5RJEFG44.2QYNE8R6J2GMP@iki.fi>
On Thu Sep 26, 2024 at 4:47 AM EEST, Jarkko Sakkinen wrote:
> On Thu Sep 26, 2024 at 3:38 AM EEST, Kai Huang wrote:
> >
> >
> > On 26/09/2024 12:33 pm, Jarkko Sakkinen wrote:
> > > On Thu Sep 26, 2024 at 3:07 AM EEST, Kai Huang wrote:
> > >>
> > >>
> > >> On 23/09/2024 7:48 pm, Jarkko Sakkinen wrote:
> > >>> On Sun Sep 22, 2024 at 7:57 PM EEST, Jarkko Sakkinen wrote:
> > >>>>> On Sun Sep 22, 2024 at 7:27 PM EEST, Jarkko Sakkinen wrote:
> > >>>>>> Hi
> > >>>>>>
> > >>>>>> I started to look into this old issue with mm subsystem and SGX, i.e.
> > >>>>>> can we make SGX VMA's to merge together?
> > >>>>>>
> > >>>>>> This demonstrates the problem pretty well:
> > >>>>>>
> > >>>>>> https://lore.kernel.org/linux-sgx/884c7ea454cf2eb0ba2e95f7c25bd42018824f97.camel@kernel.org/
> > >>>>>>
> > >>>>>> It was result of brk() syscall being applied a few times.
> > >>>>
> > >>>> Briging some context here. This can be fixed in the run-time by book
> > >>>> keeping the ranges and doing unmapping/mapping. I guess this goes
> > >>>> beyond what mm should support?
> > >>>>
> > >>>> I thought to plain check this as it has been two years since my last
> > >>>> query on topic (if we could improve either the driver or mm somehow).
> > >>>
> > >>> In the past I've substituted kernel's mm merge code with user space
> > >>> replacement:
> > >>>
> > >>> https://github.com/enarx/mmledger/blob/main/src/lib.rs
> > >>>
> > >>> It's essentially a reimplementation of al stuff that goes into
> > >>> mm/mmap.c's vma_merge(). I cannot recall anymore whether merges
> > >>> which map over existing ranges were working correctly, i.e. was
> > >>> the issue only concerning adjacent VMA's.
> > >>>
> > >>> What I'm looking here is that can we make some cosntraints that
> > >>> if satisfied by the pfnmap code, it could leverage the code from
> > >>> vma_merge(). Perhaps by making explicit call to vma_merge()?
> > >>> I get that implicit use moves too much responsibility to the mm
> > >>> subsystem.
> > >>>
> > >>
> > >> Hi Jarkko,
> > >>
> > >> Just want to understand more on the background:
> > >>
> > >> Are you seeing any real problem due to needing a lot of mmap()s to the
> > >> same enclave, or it is just a problem that doesn't look nice and you
> > >> want to resolve?
> > >>
> > >> I mean, this problem doesn't seem to be SGX-specific but a common one
> > >> for VMAs with VM_PFNMAP (any bit in VM_SPECIAL), e.g., from random
> > >> device drivers with mmap() support. We will need a good justification
> > >> if we want to make any core-mm change, if any, for this.
> > >
> > > It requires essentially replicating core mm in user space.
> > >
> >
> > Is there any real problem if we don't do this at all (neither in core mm
> > nor in userspace)?
>
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Just giving ridiculous answer to a ridiculous question.
You clearly started commenting w/o reading the original thread.
BR, Jarkko
next prev parent reply other threads:[~2024-09-26 1:49 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-22 16:27 VMA merging updateds? Jarkko Sakkinen
2024-09-22 16:35 ` Jarkko Sakkinen
2024-09-22 16:57 ` Jarkko Sakkinen
2024-09-23 7:48 ` Jarkko Sakkinen
2024-09-26 0:07 ` Huang, Kai
2024-09-26 0:33 ` Jarkko Sakkinen
2024-09-26 0:38 ` Jarkko Sakkinen
2024-09-26 0:53 ` Huang, Kai
2024-09-26 0:38 ` Huang, Kai
2024-09-26 1:47 ` Jarkko Sakkinen
2024-09-26 1:48 ` Jarkko Sakkinen [this message]
2024-09-26 10:02 ` Jarkko Sakkinen
2024-09-27 17:39 ` Lorenzo Stoakes
2024-09-29 22:36 ` Jarkko Sakkinen
2024-09-30 8:05 ` Lorenzo Stoakes
2024-10-09 14:03 ` Jarkko Sakkinen
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