Commit aaba098f authored by Andrew Murray's avatar Andrew Murray Committed by Will Deacon
Browse files

arm64: HWCAP: add support for AT_HWCAP2 



As we will exhaust the first 32 bits of AT_HWCAP let's start
exposing AT_HWCAP2 to userspace to give us up to 64 caps.

Whilst it's possible to use the remaining 32 bits of AT_HWCAP, we
prefer to expand into AT_HWCAP2 in order to provide a consistent
view to userspace between ILP32 and LP64. However internal to the
kernel we prefer to continue to use the full space of elf_hwcap.

To reduce complexity and allow for future expansion, we now
represent hwcaps in the kernel as ordinals and use a
KERNEL_HWCAP_ prefix. This allows us to support automatic feature
based module loading for all our hwcaps.

We introduce cpu_set_feature to set hwcaps which complements the
existing cpu_have_feature helper. These helpers allow us to clean
up existing direct uses of elf_hwcap and reduce any future effort
required to move beyond 64 caps.

For convenience we also introduce cpu_{have,set}_named_feature which
makes use of the cpu_feature macro to allow providing a hwcap name
without a {KERNEL_}HWCAP_ prefix.

Signed-off-by: default avatarAndrew Murray <andrew.murray@arm.com>
[will: use const_ilog2() and tweak documentation]
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent a823c35f

Documentation/arm64/elf_hwcaps.txt

+10 −3
Original line number Diff line number Diff line
@@ -13,9 +13,9 @@ architected discovery mechanism available to userspace code at EL0. The 
kernel exposes the presence of these features to userspace through a set

of flags called hwcaps, exposed in the auxilliary vector.



Userspace software can test for features by acquiring the AT_HWCAP entry

of the auxilliary vector, and testing whether the relevant flags are

set, e.g.

Userspace software can test for features by acquiring the AT_HWCAP or

AT_HWCAP2 entry of the auxiliary vector, and testing whether the relevant

flags are set, e.g.



bool floating_point_is_present(void)

{
@@ -194,3 +194,10 @@ HWCAP_PACG 
    Functionality implied by ID_AA64ISAR1_EL1.GPA == 0b0001 or

    ID_AA64ISAR1_EL1.GPI == 0b0001, as described by

    Documentation/arm64/pointer-authentication.txt.





4. Unused AT_HWCAP bits

-----------------------



For interoperation with userspace, the kernel guarantees that bits 62

and 63 of AT_HWCAP will always be returned as 0.

arch/arm64/crypto/aes-ce-ccm-glue.c

+1 −1
Original line number Diff line number Diff line
@@ -372,7 +372,7 @@ static struct aead_alg ccm_aes_alg = { 


static int __init aes_mod_init(void)

{

	if (!(elf_hwcap & HWCAP_AES))

	if (!cpu_have_named_feature(AES))

		return -ENODEV;

	return crypto_register_aead(&ccm_aes_alg);

}

arch/arm64/crypto/aes-neonbs-glue.c

+1 −1
Original line number Diff line number Diff line
@@ -440,7 +440,7 @@ static int __init aes_init(void) 
	int err;

	int i;



	if (!(elf_hwcap & HWCAP_ASIMD))

	if (!cpu_have_named_feature(ASIMD))

		return -ENODEV;



	err = crypto_register_skciphers(aes_algs, ARRAY_SIZE(aes_algs));

arch/arm64/crypto/chacha-neon-glue.c

+1 −1
Original line number Diff line number Diff line
@@ -173,7 +173,7 @@ static struct skcipher_alg algs[] = { 


static int __init chacha_simd_mod_init(void)

{

	if (!(elf_hwcap & HWCAP_ASIMD))

	if (!cpu_have_named_feature(ASIMD))

		return -ENODEV;



	return crypto_register_skciphers(algs, ARRAY_SIZE(algs));

arch/arm64/crypto/crct10dif-ce-glue.c

+2 −2
Original line number Diff line number Diff line
@@ -101,7 +101,7 @@ static struct shash_alg crc_t10dif_alg[] = {{ 


static int __init crc_t10dif_mod_init(void)

{

	if (elf_hwcap & HWCAP_PMULL)

	if (cpu_have_named_feature(PMULL))

		return crypto_register_shashes(crc_t10dif_alg,

					       ARRAY_SIZE(crc_t10dif_alg));

	else
@@ -111,7 +111,7 @@ static int __init crc_t10dif_mod_init(void) 


static void __exit crc_t10dif_mod_exit(void)

{

	if (elf_hwcap & HWCAP_PMULL)

	if (cpu_have_named_feature(PMULL))

		crypto_unregister_shashes(crc_t10dif_alg,

					  ARRAY_SIZE(crc_t10dif_alg));

	else

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