From: Nathan Lynch <nathanl@linux.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@lists.ozlabs.org
Cc: aik@ozlabs.ru, 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: Wed, 20 Jan 2021 18:26:17 -0600 [thread overview]
Message-ID: <87v9brw2xi.fsf@linux.ibm.com> (raw)
In-Reply-To: <87czxzrel3.fsf@mpe.ellerman.id.au>
Michael Ellerman <mpe@ellerman.id.au> writes:
> Nathan Lynch <nathanl@linux.ibm.com> writes:
>> Michael Ellerman <mpe@ellerman.id.au> writes:
>>> Nathan Lynch <nathanl@linux.ibm.com> writes:
>>>> 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.
>>>
>>> Why does the size of the first memory block matter for radix?
>>
>> Here is my understanding: in the platform architecture, the size of the
>> first memory block equals the RMA, regardless of the MMU mode. It just
>> so happens that when using radix, Linux can pass ibm,configure-connector
>> a work area address outside of the RMA because the allocation
>> constraints for the work area are computed differently. It would be
>> wrong of the OS to pass RTAS arguments outside of this region with hash
>> MMU as well.
>
> If that's the requirement then shouldn't we be adjusting ppc64_rma_size?
> Otherwise aren't other uses of ppc64_rma_size going to run into similar
> problems.
Not all allocations limited by ppc64_rma_size set up memory that is
passed to RTAS though, do they? e.g. emergency_stack_init and
init_fallback_flush? Those shouldn't be confined to the first LMB
unnecessarily.
That's why I'm thinking what I've written here should be generalized a
bit and placed in an early allocator function that can be used to set up
the user region and the per-cpu reentrant RTAS argument buffers
(see allocate_paca_ptrs/new_rtas_args). So far those two sites are the
only ones I'm convinced need attention.
prev parent reply other threads:[~2021-01-21 0:28 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
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 [this message]
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