From: Michael Ellerman <mpe@ellerman.id.au>
To: Dave Hansen <dave.hansen@intel.com>,
Ram Pai <linuxram@us.ibm.com>,
mingo@redhat.com, akpm@linux-foundation.org, corbet@lwn.net,
arnd@arndb.de
Cc: linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org,
x86@kernel.org, linux-arch@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org, benh@kernel.crashing.org,
paulus@samba.org, khandual@linux.vnet.ibm.com,
aneesh.kumar@linux.vnet.ibm.com, bsingharora@gmail.com,
hbabu@us.ibm.com, mhocko@kernel.org, bauerman@linux.vnet.ibm.com,
ebiederm@xmission.com
Subject: Re: [PATCH v9 29/51] mm/mprotect, powerpc/mm/pkeys, x86/mm/pkeys: Add sysfs interface
Date: Tue, 19 Dec 2017 21:50:24 +1100 [thread overview]
Message-ID: <877etj9ekv.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <bbc5593e-31ec-183a-01a5-1a253dc0c275@intel.com>
Dave Hansen <dave.hansen@intel.com> writes:
> On 11/06/2017 12:57 AM, Ram Pai wrote:
>> Expose useful information for programs using memory protection keys.
>> Provide implementation for powerpc and x86.
>>
>> On a powerpc system with pkeys support, here is what is shown:
>>
>> $ head /sys/kernel/mm/protection_keys/*
>> ==> /sys/kernel/mm/protection_keys/disable_access_supported <==
>> true
>
> This is cute, but I don't think it should be part of the ABI. Put it in
> debugfs if you want it for cute tests. The stuff that this tells you
> can and should come from pkey_alloc() for the ABI.
Yeah I agree this is not sysfs material.
In particular the total/usable numbers are completely useless vs other
threads allocating pkeys out from under you.
> http://man7.org/linux/man-pages/man7/pkeys.7.html
>
>> Any application wanting to use protection keys needs to be able to
>> function without them. They might be unavailable because the
>> hardware that the application runs on does not support them, the
>> kernel code does not contain support, the kernel support has been
>> disabled, or because the keys have all been allocated, perhaps by a
>> library the application is using. It is recommended that
>> applications wanting to use protection keys should simply call
>> pkey_alloc(2) and test whether the call succeeds, instead of
>> attempting to detect support for the feature in any other way.
>
> Do you really not have standard way on ppc to say whether hardware
> features are supported by the kernel? For instance, how do you know if
> a given set of registers are known to and are being context-switched by
> the kernel?
Yes we do, we emit feature bits in the AT_HWCAP entry of the aux vector,
same as some other architectures.
But I don't see the need to use a feature bit for pkeys. If they're not
supported then pkey_alloc() will just always fail. Apps have to handle
that anyway because keys are a finite resource.
cheers
next prev parent reply other threads:[~2017-12-19 10:50 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-06 8:56 [PATCH v9 00/51] powerpc, mm: Memory Protection Keys Ram Pai
2017-11-06 8:56 ` [PATCH v9 01/51] mm, powerpc, x86: define VM_PKEY_BITx bits if CONFIG_ARCH_HAS_PKEYS is enabled Ram Pai
2017-11-06 8:56 ` [PATCH v9 02/51] mm, powerpc, x86: introduce an additional vma bit for powerpc pkey Ram Pai
2017-11-06 8:56 ` [PATCH v9 03/51] powerpc: initial pkey plumbing Ram Pai
2017-11-06 8:56 ` [PATCH v9 04/51] powerpc: track allocation status of all pkeys Ram Pai
2017-11-06 8:56 ` [PATCH v9 05/51] powerpc: helper function to read, write AMR, IAMR, UAMOR registers Ram Pai
2017-11-06 8:56 ` [PATCH v9 06/51] powerpc: helper functions to initialize AMR, IAMR and " Ram Pai
2017-11-06 8:56 ` [PATCH v9 07/51] powerpc: cleanup AMR, IAMR when a key is allocated or freed Ram Pai
2017-11-06 8:57 ` [PATCH v9 08/51] powerpc: implementation for arch_set_user_pkey_access() Ram Pai
2017-11-06 8:57 ` [PATCH v9 09/51] powerpc: ability to create execute-disabled pkeys Ram Pai
2017-11-06 8:57 ` [PATCH v9 10/51] powerpc: store and restore the pkey state across context switches Ram Pai
2017-11-06 8:57 ` [PATCH v9 11/51] powerpc: introduce execute-only pkey Ram Pai
2017-11-06 8:57 ` [PATCH v9 12/51] powerpc: ability to associate pkey to a vma Ram Pai
2017-11-06 8:57 ` [PATCH v9 13/51] powerpc: implementation for arch_override_mprotect_pkey() Ram Pai
2017-11-06 8:57 ` [PATCH v9 14/51] powerpc: map vma key-protection bits to pte key bits Ram Pai
2017-11-06 8:57 ` [PATCH v9 15/51] powerpc: Program HPTE key protection bits Ram Pai
2017-11-06 8:57 ` [PATCH v9 16/51] powerpc: helper to validate key-access permissions of a pte Ram Pai
2017-11-06 8:57 ` [PATCH v9 17/51] powerpc: check key protection for user page access Ram Pai
2017-11-06 8:57 ` [PATCH v9 18/51] powerpc: implementation for arch_vma_access_permitted() Ram Pai
2017-11-06 8:57 ` [PATCH v9 19/51] powerpc: Handle exceptions caused by pkey violation Ram Pai
2017-11-06 8:57 ` [PATCH v9 20/51] powerpc: introduce get_mm_addr_key() helper Ram Pai
2017-11-06 8:57 ` [PATCH v9 21/51] powerpc: Deliver SEGV signal on pkey violation Ram Pai
2017-11-06 8:57 ` [PATCH v9 22/51] powerpc/ptrace: Add memory protection key regset Ram Pai
2017-11-06 8:57 ` [PATCH v9 23/51] powerpc: Enable pkey subsystem Ram Pai
2017-11-13 0:54 ` Ram Pai
2017-11-06 8:57 ` [PATCH v9 24/51] powerpc: sys_pkey_alloc() and sys_pkey_free() system calls Ram Pai
2017-11-06 8:57 ` [PATCH v9 25/51] powerpc: sys_pkey_mprotect() system call Ram Pai
2017-11-06 8:57 ` [PATCH v9 26/51] powerpc: add sys_pkey_modify() " Ram Pai
2017-11-06 8:57 ` [PATCH v9 27/51] mm, x86 : introduce arch_pkeys_enabled() Ram Pai
2017-11-06 8:57 ` [PATCH v9 28/51] mm: display pkey in smaps if arch_pkeys_enabled() is true Ram Pai
2017-11-06 8:57 ` [PATCH v9 29/51] mm/mprotect, powerpc/mm/pkeys, x86/mm/pkeys: Add sysfs interface Ram Pai
2017-12-18 18:54 ` Dave Hansen
2017-12-18 22:18 ` Ram Pai
2017-12-18 22:28 ` Dave Hansen
2017-12-18 23:15 ` Ram Pai
2017-12-19 8:31 ` Gabriel Paubert
2017-12-19 16:22 ` Ram Pai
2017-12-19 21:34 ` Benjamin Herrenschmidt
2017-12-20 17:50 ` Ram Pai
2017-12-20 22:49 ` Benjamin Herrenschmidt
2017-12-19 10:50 ` Michael Ellerman [this message]
2017-12-19 16:32 ` Ram Pai
2017-11-06 8:57 ` [PATCH v9 30/51] Documentation/x86: Move protecton key documentation to arch neutral directory Ram Pai
2017-11-06 8:57 ` [PATCH v9 31/51] Documentation/vm: PowerPC specific updates to memory protection keys Ram Pai
2017-11-06 8:57 ` [PATCH v9 32/51] selftest/x86: Move protecton key selftest to arch neutral directory Ram Pai
2017-11-06 8:57 ` [PATCH v9 33/51] selftest/vm: rename all references to pkru to a generic name Ram Pai
2017-11-06 8:57 ` [PATCH v9 34/51] selftest/vm: move generic definitions to header file Ram Pai
2017-11-06 8:57 ` [PATCH v9 35/51] selftest/vm: typecast the pkey register Ram Pai
2017-11-06 8:57 ` [PATCH v9 36/51] selftest/vm: generic function to handle shadow key register Ram Pai
2017-11-06 8:57 ` [PATCH v9 37/51] selftest/vm: fix the wrong assert in pkey_disable_set() Ram Pai
2017-11-06 8:57 ` [PATCH v9 38/51] selftest/vm: fixed bugs in pkey_disable_clear() Ram Pai
2017-11-06 8:57 ` [PATCH v9 39/51] selftest/vm: clear the bits in shadow reg when a pkey is freed Ram Pai
2017-11-06 8:57 ` [PATCH v9 40/51] selftest/vm: fix alloc_random_pkey() to make it really random Ram Pai
2017-11-06 8:57 ` [PATCH v9 41/51] selftest/vm: introduce two arch independent abstraction Ram Pai
2017-11-06 8:57 ` [PATCH v9 42/51] selftest/vm: pkey register should match shadow pkey Ram Pai
2017-11-06 8:57 ` [PATCH v9 43/51] selftest/vm: generic cleanup Ram Pai
2017-11-06 8:57 ` [PATCH v9 44/51] selftest/vm: powerpc implementation for generic abstraction Ram Pai
2017-11-09 18:47 ` Breno Leitao
2017-11-09 23:37 ` Ram Pai
2017-11-10 11:36 ` Breno Leitao
2017-11-06 8:57 ` [PATCH v9 45/51] selftest/vm: fix an assertion in test_pkey_alloc_exhaust() Ram Pai
2017-11-06 8:57 ` [PATCH v9 46/51] selftest/vm: associate key on a mapped page and detect access violation Ram Pai
2017-11-06 8:57 ` [PATCH v9 47/51] selftest/vm: associate key on a mapped page and detect write violation Ram Pai
2017-11-06 8:57 ` [PATCH v9 48/51] selftest/vm: detect write violation on a mapped access-denied-key page Ram Pai
2017-11-06 8:57 ` [PATCH v9 49/51] selftest/vm: sub-page allocator Ram Pai
2017-11-06 8:57 ` [PATCH v9 50/51] selftests/powerpc: Add ptrace tests for Protection Key register Ram Pai
2017-11-06 8:57 ` [PATCH v9 51/51] selftests/powerpc: Add core file test " Ram Pai
2017-11-06 21:28 ` [PATCH v9 00/51] powerpc, mm: Memory Protection Keys Florian Weimer
2017-11-07 1:22 ` Ram Pai
2017-11-07 7:32 ` Florian Weimer
2017-11-07 22:39 ` Ram Pai
2017-11-07 22:47 ` Dave Hansen
2017-11-07 23:44 ` Ram Pai
2017-11-09 22:23 ` Ram Pai
2017-11-10 18:10 ` Christophe LEROY
2017-11-12 20:45 ` Ram Pai
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