KVM ARM Archive on lore.kernel.org
 help / color / Atom feed
From: Catalin Marinas <catalin.marinas@arm.com>
To: Guo Ren <guoren@kernel.org>
Cc: aou@eecs.berkeley.edu, Marc Zyngier <marc.zyngier@arm.com>,
	Anup Patel <anup.Patel@wdc.com>,
	will.deacon@arm.com, linux-kernel@vger.kernel.org,
	rppt@linux.ibm.com, hch@infradead.org, Atish.Patra@wdc.com,
	Julien Grall <julien.grall@arm.com>,
	Palmer Dabbelt <palmer@sifive.com>,
	gary@garyguo.net, paul.walmsley@sifive.com,
	linux-riscv@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file
Date: Fri, 21 Jun 2019 15:16:07 +0100
Message-ID: <20190621141606.GF18954@arrakis.emea.arm.com> (raw)
In-Reply-To: <CAJF2gTStSR7Jmu7=HaO5Wxz=Zn8A5-RD8ktori3oKEhM9vozAA@mail.gmail.com>

On Wed, Jun 19, 2019 at 07:51:03PM +0800, Guo Ren wrote:
> On Wed, Jun 19, 2019 at 4:54 PM Julien Grall <julien.grall@arm.com> wrote:
> > On 6/19/19 9:07 AM, Guo Ren wrote:
> > > Move arm asid allocator code in a generic one is a agood idea, I've
> > > made a patchset for C-SKY and test is on processing, See:
> > > https://lore.kernel.org/linux-csky/1560930553-26502-1-git-send-email-guoren@kernel.org/
> > >
> > > If you plan to seperate it into generic one, I could co-work with you.
> >
> > Was the ASID allocator work out of box on C-Sky?
> 
> Almost done, but one question:
> arm64 remove the code in switch_mm:
>   cpumask_clear_cpu(cpu, mm_cpumask(prev));
>   cpumask_set_cpu(cpu, mm_cpumask(next));
> 
> Why? Although arm64 cache operations could affect all harts with CTC
> method of interconnect, I think we should keep these code for
> primitive integrity in linux. Because cpu_bitmap is in mm_struct
> instead of mm->context.

We didn't have a use for this in the arm64 code, so no point in
maintaining the mm_cpumask. On some arm32 systems (ARMv6) with no
hardware broadcast of some TLB/cache operations, we use it to track
where the task has run to issue IPI for TLB invalidation or some
deferred I-cache invalidation.

(there was also a potential optimisation on arm64 to avoid broadcast
TLBI if the task only ran on a single CPU but Will found that was rarely
the case on an SMP system because of rebalancing happening during
execve(), ending up with two bits set in the mm_cpumask)

The way you use it on csky is different from how it is done on arm. It
seems to clear the mask for the scheduled out (prev) task but this
wouldn't work on arm(64) since the TLB still contains prev entries
tagged with the scheduled out ASID. Whether it matters, I guess it
depends on the specifics of your hardware.

While the algorithm may seem fairly generic, the semantics have a few
corner cases specific to each architecture. See [1] for a description of
the semantics we need on arm64 (CnP is a feature where the hardware
threads of the same core can share the TLB; the original algorithm
violated the requirements when this feature was enabled).

BTW, if you find the algorithm fairly straightforward ;), see this
bug-fix which took a formal model to identify: a8ffaaa060b8 ("arm64:
asid: Do not replace active_asids if already 0").

[1] https://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/kernel-tla.git/tree/asidalloc.tla#n79

-- 
Catalin
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

  parent reply index

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-21 16:36 [PATCH RFC 00/14] kvm/arm: Align the VMID allocation with the arm64 ASID one Julien Grall
2019-03-21 16:36 ` [PATCH RFC 01/14] arm64/mm: Introduce asid_info structure and move asid_generation/asid_map to it Julien Grall
2019-03-21 17:03   ` Suzuki K Poulose
2019-03-21 17:27     ` Julien Grall
2019-03-21 16:36 ` [PATCH RFC 02/14] arm64/mm: Move active_asids and reserved_asids to asid_info Julien Grall
2019-03-21 16:36 ` [PATCH RFC 03/14] arm64/mm: Move bits " Julien Grall
2019-03-21 16:36 ` [PATCH RFC 04/14] arm64/mm: Move the variable lock and tlb_flush_pending " Julien Grall
2019-03-21 16:36 ` [PATCH RFC 05/14] arm64/mm: Remove dependency on MM in new_context Julien Grall
2019-03-21 16:36 ` [PATCH RFC 06/14] arm64/mm: Store the number of asid allocated per context Julien Grall
2019-03-21 16:36 ` [PATCH RFC 07/14] arm64/mm: Introduce NUM_ASIDS Julien Grall
2019-03-21 16:36 ` [PATCH RFC 08/14] arm64/mm: Split asid_inits in 2 parts Julien Grall
2019-03-21 16:36 ` [PATCH RFC 09/14] arm64/mm: Split the function check_and_switch_context in 3 parts Julien Grall
2019-03-21 16:36 ` [PATCH RFC 10/14] arm64/mm: Introduce a callback to flush the local context Julien Grall
2019-03-21 16:36 ` [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file Julien Grall
2019-06-05 16:56   ` Julien Grall
2019-06-05 20:41     ` Palmer Dabbelt
2019-06-11  1:56       ` Gary Guo
2019-06-19  8:07     ` Guo Ren
2019-06-19  8:54       ` Julien Grall
2019-06-19  9:12         ` Will Deacon
2019-06-19 12:18           ` Guo Ren
2019-06-19 12:39             ` Will Deacon
2019-06-20  9:33               ` Guo Ren
2019-06-24 10:40                 ` Will Deacon
2019-06-25  7:25                   ` Palmer Dabbelt
2019-09-07 23:52                   ` Guo Ren
2019-09-12 14:02                     ` Will Deacon
2019-09-12 14:59                       ` Guo Ren
2019-09-13  7:13                         ` Guo Ren
2019-09-14  8:49                           ` Guo Ren
2019-09-16 12:57                           ` Jean-Philippe Brucker
2019-09-19 13:07                             ` Guo Ren
2019-09-19 15:18                               ` Jean-Philippe Brucker
2019-09-20  0:07                                 ` Guo Ren
2019-09-20  7:18                                   ` Jean-Philippe Brucker
2019-09-14 14:01                       ` Palmer Dabbelt
2019-09-15  5:03                         ` Anup Patel
2019-09-16 18:18                           ` Will Deacon
2019-09-16 18:28                             ` Palmer Dabbelt
2019-09-17  3:42                             ` Anup Patel
2019-09-19 13:36                               ` Guo Ren
2019-06-19 11:51         ` Guo Ren
2019-06-19 12:52           ` Julien Grall
2019-06-21 14:16           ` Catalin Marinas [this message]
2019-06-23 16:35             ` Guo Ren
2019-06-24 10:22               ` Will Deacon
2019-06-27  9:41                 ` qi.fuli
2019-06-27 10:26                   ` Will Deacon
2019-06-24 15:38               ` Catalin Marinas
2019-06-30  4:29                 ` Guo Ren
2019-07-01  9:17                   ` Catalin Marinas
2019-07-16  3:31                     ` Guo Ren
2019-07-22 16:38                       ` Catalin Marinas
2019-03-21 16:36 ` [PATCH RFC 12/14] arm64/lib: asid: Allow user to update the context under the lock Julien Grall
2019-03-21 16:36 ` [PATCH RFC 13/14] arm/kvm: Introduce a new VMID allocator Julien Grall
2019-03-21 16:36 ` [PATCH RFC 14/14] kvm/arm: Align the VMID allocation with the arm64 ASID one Julien Grall

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190621141606.GF18954@arrakis.emea.arm.com \
    --to=catalin.marinas@arm.com \
    --cc=Atish.Patra@wdc.com \
    --cc=anup.Patel@wdc.com \
    --cc=aou@eecs.berkeley.edu \
    --cc=gary@garyguo.net \
    --cc=guoren@kernel.org \
    --cc=hch@infradead.org \
    --cc=julien.grall@arm.com \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=marc.zyngier@arm.com \
    --cc=palmer@sifive.com \
    --cc=paul.walmsley@sifive.com \
    --cc=rppt@linux.ibm.com \
    --cc=will.deacon@arm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM ARM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvmarm/0 kvmarm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvmarm kvmarm/ https://lore.kernel.org/kvmarm \
		kvmarm@lists.cs.columbia.edu
	public-inbox-index kvmarm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/edu.columbia.cs.lists.kvmarm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git