diff options
| author | Christophe Leroy <christophe.leroy@csgroup.eu> | 2023-07-11 17:59:13 +0200 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2023-08-02 22:22:17 +1000 |
| commit | 880df2d46a3f23f30f954f6e64c576d7f411cc46 (patch) | |
| tree | 6d0e8a8f38f1d8656dedb8167e4c3ad910dde9a3 /arch/powerpc/include/asm/nohash/32/kup-8xx.h | |
| parent | 6eaae198076080886b9e7d57f4ae06fa782f90ef (diff) | |
powerpc/kuap: Avoid unnecessary reads of MD_AP
A disassembly of interrupt_exit_kernel_prepare() shows a useless read
of MD_AP register. This is shown by r9 being re-used immediately without
doing anything with the value read.
c000e0e0: 60 00 00 00 nop
c000e0e4: ===> 7d 3a c2 a6 mfmd_ap r9 <====
c000e0e8: 7d 20 00 a6 mfmsr r9
c000e0ec: 7c 51 13 a6 mtspr 81,r2
c000e0f0: 81 3f 00 84 lwz r9,132(r31)
c000e0f4: 71 29 80 00 andi. r9,r9,32768
kuap_get_and_assert_locked() is paired with kuap_kernel_restore()
and are only used in interrupt_exit_kernel_prepare(). The value
returned by kuap_get_and_assert_locked() is only used by
kuap_kernel_restore().
On 8xx, kuap_kernel_restore() doesn't use the value read by
kuap_get_and_assert_locked() so modify kuap_get_and_assert_locked()
to not perform the read of MD_AP and return 0 instead.
The same applies on BOOKE.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/bcbc84c2dd90bb1021da792b1968cdc22112dad8.1689091022.git.christophe.leroy@csgroup.eu
Diffstat (limited to 'arch/powerpc/include/asm/nohash/32/kup-8xx.h')
| -rw-r--r-- | arch/powerpc/include/asm/nohash/32/kup-8xx.h | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h index c44d97751723..8579210f2a6a 100644 --- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h +++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h @@ -41,14 +41,10 @@ static inline void __kuap_kernel_restore(struct pt_regs *regs, unsigned long kua static inline unsigned long __kuap_get_and_assert_locked(void) { - unsigned long kuap; - - kuap = mfspr(SPRN_MD_AP); - if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG)) - WARN_ON_ONCE(kuap >> 16 != MD_APG_KUAP >> 16); + WARN_ON_ONCE(mfspr(SPRN_MD_AP) >> 16 != MD_APG_KUAP >> 16); - return kuap; + return 0; } static inline void __allow_user_access(void __user *to, const void __user *from, |