linuxppc-dev.lists.ozlabs.org archive mirror
 help / color / mirror / Atom feed
From: Nathan Lynch <nathanl@linux.ibm.com>
To: Alexey Kardashevskiy <aik@ozlabs.ru>, linuxppc-dev@lists.ozlabs.org
Cc: tyreld@linux.ibm.com, brking@linux.ibm.com, ajd@linux.ibm.com,
	aneesh.kumar@linux.ibm.com
Subject: Re: [PATCH 6/6] powerpc/rtas: constrain user region allocation to RMA
Date: Fri, 15 Jan 2021 09:38:22 -0600	[thread overview]
Message-ID: <87czy6xlap.fsf@linux.ibm.com> (raw)
In-Reply-To: <5276937f-b72a-89ba-d0d8-19e4be55ae35@ozlabs.ru>

Alexey Kardashevskiy <aik@ozlabs.ru> writes:
> On 15/01/2021 09:00, Nathan Lynch wrote:
>> Memory locations passed as arguments from the OS to RTAS usually need
>> to be addressable in 32-bit mode and must reside in the Real Mode
>> Area. On PAPR guests, the RMA starts at logical address 0 and is the
>> first logical memory block reported in the LPAR’s device tree.
>> 
>> On powerpc targets with RTAS, Linux makes available to user space a
>> region of memory suitable for arguments to be passed to RTAS via
>> sys_rtas(). This region (rtas_rmo_buf) is allocated via the memblock
>> API during boot in order to ensure that it satisfies the requirements
>> described above.
>> 
>> With radix MMU, the upper limit supplied to the memblock allocation
>> can exceed the bounds of the first logical memory block, since
>> ppc64_rma_size is ULONG_MAX and RTAS_INSTANTIATE_MAX is 1GB. (512MB is
>> a common size of the first memory block according to a small sample of
>> LPARs I have checked.) This leads to failures when user space invokes
>> an RTAS function that uses a work area, such as
>> ibm,configure-connector.
>> 
>> Alter the determination of the upper limit for rtas_rmo_buf's
>> allocation to consult the device tree directly, ensuring placement
>> within the RMA regardless of the MMU in use.
>
> Can we tie this with RTAS (which also needs to be in RMA) and simply add 
> extra 64K in prom_instantiate_rtas() and advertise this address 
> (ALIGH_UP(rtas-base + rtas-size, PAGE_SIZE)) to the user space? We do 
> not need this RMO area before that point.

Can you explain more about what advantage that would bring? I'm not
seeing it. It's a more significant change than what I've written
here. Would it interact well with kexec?

> And probably do the same with per-cpu RTAS argument structures mentioned 
> in the cover letter?

I don't think so, since those need to be allocated with the pacas and
limited to the maximum possible CPUs, which is discovered by the kernel
much later.

But maybe I misunderstand what you're suggesting.

  reply	other threads:[~2021-01-15 15:41 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-14 21:59 [PATCH 0/6] powerpc/rtas: miscellaneous cleanups, user region allocation Nathan Lynch
2021-01-14 21:59 ` [PATCH 1/6] powerpc/rtas: improve ppc_rtas_rmo_buf_show documentation Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:50   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 2/6] powerpc/rtas-proc: remove unused RMO_READ_BUF_MAX Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:52   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 3/6] powerpc/rtas: remove ibm_suspend_me_token Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:52   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 4/6] powerpc/rtas: move syscall filter setup into separate function Nathan Lynch
2021-01-15  4:39   ` Alexey Kardashevskiy
2021-01-15 16:04     ` Nathan Lynch
2021-01-15  5:49   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 5/6] powerpc/rtas: rename RTAS_RMOBUF_MAX to RTAS_USER_REGION_SIZE Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15 15:56     ` Nathan Lynch
2021-01-18  4:15       ` Alexey Kardashevskiy
2021-01-20  1:17         ` Nathan Lynch
2021-01-20  5:05           ` Alexey Kardashevskiy
2021-01-21 15:17             ` Nathan Lynch
2021-01-15  6:10   ` Andrew Donnellan
2021-01-15 12:04   ` kernel test robot
2021-01-14 22:00 ` [PATCH 6/6] powerpc/rtas: constrain user region allocation to RMA Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15 15:38     ` Nathan Lynch [this message]
2021-01-18  4:12       ` Alexey Kardashevskiy
2021-01-20  0:39         ` Nathan Lynch
2021-01-20  4:49           ` Alexey Kardashevskiy
2021-01-20 12:06           ` Michael Ellerman
2021-01-21 15:27             ` Nathan Lynch
2021-01-23  1:54               ` Alexey Kardashevskiy
2021-01-19  9:00   ` Michael Ellerman
2021-01-19 21:00     ` Nathan Lynch
2021-01-20 12:13       ` Michael Ellerman
2021-01-21  0:26         ` Nathan Lynch

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=87czy6xlap.fsf@linux.ibm.com \
    --to=nathanl@linux.ibm.com \
    --cc=aik@ozlabs.ru \
    --cc=ajd@linux.ibm.com \
    --cc=aneesh.kumar@linux.ibm.com \
    --cc=brking@linux.ibm.com \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=tyreld@linux.ibm.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).