From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Alex Ghiti <alex@ghiti.fr>, Palmer Dabbelt <palmer@dabbelt.com>
Cc: mpe@ellerman.id.au, paulus@samba.org,
Paul Walmsley <paul.walmsley@sifive.com>,
aou@eecs.berkeley.edu, Anup Patel <Anup.Patel@wdc.com>,
Atish Patra <Atish.Patra@wdc.com>,
zong.li@sifive.com, linux-kernel@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
linux-mm@kvack.org
Subject: Re: [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone
Date: Wed, 22 Jul 2020 09:11:02 +1000 [thread overview]
Message-ID: <54af168083aee9dbda1b531227521a26b77ba2c8.camel@kernel.crashing.org> (raw)
In-Reply-To: <7cb2285e-68ba-6827-5e61-e33a4b65ac03@ghiti.fr>
On Tue, 2020-07-21 at 14:36 -0400, Alex Ghiti wrote:
> > > I guess I don't understand why this is necessary at all.
> > > Specifically: why
> > > can't we just relocate the kernel within the linear map? That would
> > > let the
> > > bootloader put the kernel wherever it wants, modulo the physical
> > > memory size we
> > > support. We'd need to handle the regions that are coupled to the
> > > kernel's
> > > execution address, but we could just put them in an explicit memory
> > > region
> > > which is what we should probably be doing anyway.
> >
> > Virtual relocation in the linear mapping requires to move the kernel
> > physically too. Zong implemented this physical move in its KASLR RFC
> > patchset, which is cumbersome since finding an available physical spot
> > is harder than just selecting a virtual range in the vmalloc range.
> >
> > In addition, having the kernel mapping in the linear mapping prevents
> > the use of hugepage for the linear mapping resulting in performance loss
> > (at least for the GB that encompasses the kernel).
> >
> > Why do you find this "ugly" ? The vmalloc region is just a bunch of
> > available virtual addresses to whatever purpose we want, and as noted by
> > Zong, arm64 uses the same scheme.
I don't get it :-)
At least on powerpc we move the kernel in the linear mapping and it
works fine with huge pages, what is your problem there ? You rely on
punching small-page size holes in there ?
At least in the old days, there were a number of assumptions that
the kernel text/data/bss resides in the linear mapping.
If you change that you need to ensure that it's still physically
contiguous and you'll have to tweak __va and __pa, which might induce
extra overhead.
Cheers,
Ben.
WARNING: multiple messages have this Message-ID (diff)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Alex Ghiti <alex@ghiti.fr>, Palmer Dabbelt <palmer@dabbelt.com>
Cc: aou@eecs.berkeley.edu, linux-mm@kvack.org, mpe@ellerman.id.au,
Anup Patel <Anup.Patel@wdc.com>,
linux-kernel@vger.kernel.org, Atish Patra <Atish.Patra@wdc.com>,
paulus@samba.org, zong.li@sifive.com,
Paul Walmsley <paul.walmsley@sifive.com>,
linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone
Date: Wed, 22 Jul 2020 09:11:02 +1000 [thread overview]
Message-ID: <54af168083aee9dbda1b531227521a26b77ba2c8.camel@kernel.crashing.org> (raw)
In-Reply-To: <7cb2285e-68ba-6827-5e61-e33a4b65ac03@ghiti.fr>
On Tue, 2020-07-21 at 14:36 -0400, Alex Ghiti wrote:
> > > I guess I don't understand why this is necessary at all.
> > > Specifically: why
> > > can't we just relocate the kernel within the linear map? That would
> > > let the
> > > bootloader put the kernel wherever it wants, modulo the physical
> > > memory size we
> > > support. We'd need to handle the regions that are coupled to the
> > > kernel's
> > > execution address, but we could just put them in an explicit memory
> > > region
> > > which is what we should probably be doing anyway.
> >
> > Virtual relocation in the linear mapping requires to move the kernel
> > physically too. Zong implemented this physical move in its KASLR RFC
> > patchset, which is cumbersome since finding an available physical spot
> > is harder than just selecting a virtual range in the vmalloc range.
> >
> > In addition, having the kernel mapping in the linear mapping prevents
> > the use of hugepage for the linear mapping resulting in performance loss
> > (at least for the GB that encompasses the kernel).
> >
> > Why do you find this "ugly" ? The vmalloc region is just a bunch of
> > available virtual addresses to whatever purpose we want, and as noted by
> > Zong, arm64 uses the same scheme.
I don't get it :-)
At least on powerpc we move the kernel in the linear mapping and it
works fine with huge pages, what is your problem there ? You rely on
punching small-page size holes in there ?
At least in the old days, there were a number of assumptions that
the kernel text/data/bss resides in the linear mapping.
If you change that you need to ensure that it's still physically
contiguous and you'll have to tweak __va and __pa, which might induce
extra overhead.
Cheers,
Ben.
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
WARNING: multiple messages have this Message-ID (diff)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Alex Ghiti <alex@ghiti.fr>, Palmer Dabbelt <palmer@dabbelt.com>
Cc: aou@eecs.berkeley.edu, linux-mm@kvack.org,
Anup Patel <Anup.Patel@wdc.com>,
linux-kernel@vger.kernel.org, Atish Patra <Atish.Patra@wdc.com>,
paulus@samba.org, zong.li@sifive.com,
Paul Walmsley <paul.walmsley@sifive.com>,
linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone
Date: Wed, 22 Jul 2020 09:11:02 +1000 [thread overview]
Message-ID: <54af168083aee9dbda1b531227521a26b77ba2c8.camel@kernel.crashing.org> (raw)
In-Reply-To: <7cb2285e-68ba-6827-5e61-e33a4b65ac03@ghiti.fr>
On Tue, 2020-07-21 at 14:36 -0400, Alex Ghiti wrote:
> > > I guess I don't understand why this is necessary at all.
> > > Specifically: why
> > > can't we just relocate the kernel within the linear map? That would
> > > let the
> > > bootloader put the kernel wherever it wants, modulo the physical
> > > memory size we
> > > support. We'd need to handle the regions that are coupled to the
> > > kernel's
> > > execution address, but we could just put them in an explicit memory
> > > region
> > > which is what we should probably be doing anyway.
> >
> > Virtual relocation in the linear mapping requires to move the kernel
> > physically too. Zong implemented this physical move in its KASLR RFC
> > patchset, which is cumbersome since finding an available physical spot
> > is harder than just selecting a virtual range in the vmalloc range.
> >
> > In addition, having the kernel mapping in the linear mapping prevents
> > the use of hugepage for the linear mapping resulting in performance loss
> > (at least for the GB that encompasses the kernel).
> >
> > Why do you find this "ugly" ? The vmalloc region is just a bunch of
> > available virtual addresses to whatever purpose we want, and as noted by
> > Zong, arm64 uses the same scheme.
I don't get it :-)
At least on powerpc we move the kernel in the linear mapping and it
works fine with huge pages, what is your problem there ? You rely on
punching small-page size holes in there ?
At least in the old days, there were a number of assumptions that
the kernel text/data/bss resides in the linear mapping.
If you change that you need to ensure that it's still physically
contiguous and you'll have to tweak __va and __pa, which might induce
extra overhead.
Cheers,
Ben.
next prev parent reply other threads:[~2020-07-21 23:12 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-07 7:59 [PATCH v5 0/4] vmalloc kernel mapping and relocatable kernel Alexandre Ghiti
2020-06-07 7:59 ` [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone Alexandre Ghiti
2020-06-11 21:34 ` Atish Patra
2020-06-11 21:34 ` Atish Patra
2020-06-11 21:34 ` Atish Patra
2020-06-12 12:30 ` Alex Ghiti
2020-06-12 12:30 ` Alex Ghiti
2020-06-12 12:30 ` Alex Ghiti
2020-07-09 5:05 ` Palmer Dabbelt
2020-07-09 5:05 ` Palmer Dabbelt
2020-07-09 5:05 ` Palmer Dabbelt
2020-07-09 8:15 ` Zong Li
2020-07-09 8:15 ` Zong Li
2020-07-09 8:15 ` Zong Li
2020-07-09 11:11 ` Alex Ghiti
2020-07-09 11:11 ` Alex Ghiti
2020-07-09 11:11 ` Alex Ghiti
2020-07-21 18:36 ` Alex Ghiti
2020-07-21 18:36 ` Alex Ghiti
2020-07-21 18:36 ` Alex Ghiti
2020-07-21 19:05 ` Palmer Dabbelt
2020-07-21 19:05 ` Palmer Dabbelt
2020-07-21 19:05 ` Palmer Dabbelt
2020-07-21 23:12 ` Benjamin Herrenschmidt
2020-07-21 23:12 ` Benjamin Herrenschmidt
2020-07-21 23:12 ` Benjamin Herrenschmidt
2020-07-21 23:48 ` Palmer Dabbelt
2020-07-21 23:48 ` Palmer Dabbelt
2020-07-21 23:48 ` Palmer Dabbelt
2020-07-22 2:21 ` Benjamin Herrenschmidt
2020-07-22 2:21 ` Benjamin Herrenschmidt
2020-07-22 2:21 ` Benjamin Herrenschmidt
2020-07-22 4:50 ` Michael Ellerman
2020-07-22 4:50 ` Michael Ellerman
2020-07-22 4:50 ` Michael Ellerman
2020-07-22 5:46 ` Palmer Dabbelt
2020-07-22 5:46 ` Palmer Dabbelt
2020-07-22 5:46 ` Palmer Dabbelt
2020-07-22 9:43 ` Arnd Bergmann
2020-07-22 9:43 ` Arnd Bergmann
2020-07-22 9:43 ` Arnd Bergmann
2020-07-22 9:43 ` Arnd Bergmann
2020-07-22 19:52 ` Palmer Dabbelt
2020-07-22 19:52 ` Palmer Dabbelt
2020-07-22 19:52 ` Palmer Dabbelt
2020-07-22 20:22 ` Arnd Bergmann
2020-07-22 20:22 ` Arnd Bergmann
2020-07-22 20:22 ` Arnd Bergmann
2020-07-22 20:22 ` Arnd Bergmann
2020-07-22 21:05 ` Atish Patra
2020-07-22 21:05 ` Atish Patra
2020-07-22 21:05 ` Atish Patra
2020-07-22 21:05 ` Atish Patra
2020-07-24 7:20 ` Arnd Bergmann
2020-07-24 7:20 ` Arnd Bergmann
2020-07-24 7:20 ` Arnd Bergmann
2020-07-24 7:20 ` Arnd Bergmann
2020-07-23 5:32 ` Alex Ghiti
2020-07-23 5:32 ` Alex Ghiti
2020-07-23 5:32 ` Alex Ghiti
2020-07-21 23:11 ` Benjamin Herrenschmidt [this message]
2020-07-21 23:11 ` Benjamin Herrenschmidt
2020-07-21 23:11 ` Benjamin Herrenschmidt
2020-07-21 23:36 ` Palmer Dabbelt
2020-07-21 23:36 ` Palmer Dabbelt
2020-07-21 23:36 ` Palmer Dabbelt
2020-07-23 5:36 ` Alex Ghiti
2020-07-23 5:36 ` Alex Ghiti
2020-07-23 5:36 ` Alex Ghiti
2020-07-23 5:21 ` Alex Ghiti
2020-07-23 5:21 ` Alex Ghiti
2020-07-23 5:21 ` Alex Ghiti
2020-07-23 22:33 ` Benjamin Herrenschmidt
2020-07-23 22:33 ` Benjamin Herrenschmidt
2020-07-23 22:33 ` Benjamin Herrenschmidt
2020-07-24 8:14 ` Arnd Bergmann
2020-07-24 8:14 ` Arnd Bergmann
2020-07-24 8:14 ` Arnd Bergmann
2020-07-24 8:14 ` Arnd Bergmann
2020-06-07 7:59 ` [PATCH v5 2/4] riscv: Introduce CONFIG_RELOCATABLE Alexandre Ghiti
2020-06-07 7:59 ` Alexandre Ghiti
2020-06-10 14:10 ` Jerome Forissier
2020-06-11 19:43 ` Alex Ghiti
2020-06-07 7:59 ` [PATCH v5 3/4] powerpc: Move script to check relocations at compile time in scripts/ Alexandre Ghiti
2020-06-07 7:59 ` Alexandre Ghiti
2020-06-07 7:59 ` [PATCH v5 4/4] riscv: Check relocations at compile time Alexandre Ghiti
2020-06-07 7:59 ` Alexandre Ghiti
2020-07-08 4:21 ` [PATCH v5 0/4] vmalloc kernel mapping and relocatable kernel Alex Ghiti
2020-07-08 4:21 ` Alex Ghiti
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