All of lore.kernel.org
 help / color / mirror / Atom feed
From: Michael Ellerman <mpe@ellerman.id.au>
To: Suraj Jitindar Singh <sjitindarsingh@gmail.com>,
	linuxppc-dev@lists.ozlabs.org
Cc: kvm-ppc@vger.kernel.org, david@gibson.dropbear.id.au
Subject: Re: [PATCH] powerpc: mm: Limit rma_size to 1TB when running without HV mode
Date: Mon, 15 Jul 2019 12:23:44 +1000	[thread overview]
Message-ID: <87d0ic9gsv.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <1563155904.2145.1.camel@gmail.com>

Suraj Jitindar Singh <sjitindarsingh@gmail.com> writes:
> On Fri, 2019-07-12 at 23:09 +1000, Michael Ellerman wrote:
>> Suraj Jitindar Singh <sjitindarsingh@gmail.com> writes:
>> > The virtual real mode addressing (VRMA) mechanism is used when a
>> > partition is using HPT (Hash Page Table) translation and performs
>> > real mode accesses (MSR[IR|DR] = 0) in non-hypervisor mode. In this
>> > mode effective address bits 0:23 are treated as zero (i.e. the
>> > access
>> > is aliased to 0) and the access is performed using an implicit 1TB
>> > SLB
>> > entry.
>> > 
>> > The size of the RMA (Real Memory Area) is communicated to the guest
>> > as
>> > the size of the first memory region in the device tree. And because
>> > of
>> > the mechanism described above can be expected to not exceed 1TB. In
>> > the
>> > event that the host erroneously represents the RMA as being larger
>> > than
>> > 1TB, guest accesses in real mode to memory addresses above 1TB will
>> > be
>> > aliased down to below 1TB. This means that a memory access
>> > performed in
>> > real mode may differ to one performed in virtual mode for the same
>> > memory
>> > address, which would likely have unintended consequences.
>> > 
>> > To avoid this outcome have the guest explicitly limit the size of
>> > the
>> > RMA to the current maximum, which is 1TB. This means that even if
>> > the
>> > first memory block is larger than 1TB, only the first 1TB should be
>> > accessed in real mode.
>> > 
>> > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
>> 
>> I added:
>> 
>> Fixes: c3ab300ea555 ("powerpc: Add POWER9 cputable entry")
>> Cc: stable@vger.kernel.org # v4.6+
>> 
>> 
>> Which is not exactly correct, but probably good enough?
>
> I think we actually want:
> Fixes: c610d65c0ad0 ("powerpc/pseries: lift RTAS limit for hash")
>
> Which is what actually caused it to break and for the issue to present
> itself.

Thanks, I used that instead.

cheers

WARNING: multiple messages have this Message-ID (diff)
From: Michael Ellerman <mpe@ellerman.id.au>
To: Suraj Jitindar Singh <sjitindarsingh@gmail.com>,
	linuxppc-dev@lists.ozlabs.org
Cc: kvm-ppc@vger.kernel.org, david@gibson.dropbear.id.au
Subject: Re: [PATCH] powerpc: mm: Limit rma_size to 1TB when running without HV mode
Date: Mon, 15 Jul 2019 02:23:44 +0000	[thread overview]
Message-ID: <87d0ic9gsv.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <1563155904.2145.1.camel@gmail.com>

Suraj Jitindar Singh <sjitindarsingh@gmail.com> writes:
> On Fri, 2019-07-12 at 23:09 +1000, Michael Ellerman wrote:
>> Suraj Jitindar Singh <sjitindarsingh@gmail.com> writes:
>> > The virtual real mode addressing (VRMA) mechanism is used when a
>> > partition is using HPT (Hash Page Table) translation and performs
>> > real mode accesses (MSR[IR|DR] = 0) in non-hypervisor mode. In this
>> > mode effective address bits 0:23 are treated as zero (i.e. the
>> > access
>> > is aliased to 0) and the access is performed using an implicit 1TB
>> > SLB
>> > entry.
>> > 
>> > The size of the RMA (Real Memory Area) is communicated to the guest
>> > as
>> > the size of the first memory region in the device tree. And because
>> > of
>> > the mechanism described above can be expected to not exceed 1TB. In
>> > the
>> > event that the host erroneously represents the RMA as being larger
>> > than
>> > 1TB, guest accesses in real mode to memory addresses above 1TB will
>> > be
>> > aliased down to below 1TB. This means that a memory access
>> > performed in
>> > real mode may differ to one performed in virtual mode for the same
>> > memory
>> > address, which would likely have unintended consequences.
>> > 
>> > To avoid this outcome have the guest explicitly limit the size of
>> > the
>> > RMA to the current maximum, which is 1TB. This means that even if
>> > the
>> > first memory block is larger than 1TB, only the first 1TB should be
>> > accessed in real mode.
>> > 
>> > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
>> 
>> I added:
>> 
>> Fixes: c3ab300ea555 ("powerpc: Add POWER9 cputable entry")
>> Cc: stable@vger.kernel.org # v4.6+
>> 
>> 
>> Which is not exactly correct, but probably good enough?
>
> I think we actually want:
> Fixes: c610d65c0ad0 ("powerpc/pseries: lift RTAS limit for hash")
>
> Which is what actually caused it to break and for the issue to present
> itself.

Thanks, I used that instead.

cheers

  reply	other threads:[~2019-07-15  2:25 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-10  5:20 [PATCH] powerpc: mm: Limit rma_size to 1TB when running without HV mode Suraj Jitindar Singh
2019-07-10  5:20 ` Suraj Jitindar Singh
2019-07-10  7:32 ` Satheesh Rajendran
2019-07-10  7:44   ` Satheesh Rajendran
2019-07-10 14:21 ` David Gibson
2019-07-10 14:21   ` David Gibson
2019-07-12 13:09 ` Michael Ellerman
2019-07-12 13:09   ` Michael Ellerman
2019-07-15  1:58   ` Suraj Jitindar Singh
2019-07-15  1:58     ` Suraj Jitindar Singh
2019-07-15  2:23     ` Michael Ellerman [this message]
2019-07-15  2:23       ` Michael Ellerman
2019-07-18 13:56 ` Michael Ellerman
2019-07-18 13:56   ` Michael Ellerman

Reply instructions:

You may reply publicly 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=87d0ic9gsv.fsf@concordia.ellerman.id.au \
    --to=mpe@ellerman.id.au \
    --cc=david@gibson.dropbear.id.au \
    --cc=kvm-ppc@vger.kernel.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=sjitindarsingh@gmail.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
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.