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
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@ -41,14 +41,10 @@ static inline void __kuap_kernel_restore(struct pt_regs *regs, unsigned long kua
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static inline unsigned long __kuap_get_and_assert_locked(void)
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{
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unsigned long kuap;
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kuap = mfspr(SPRN_MD_AP);
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if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG))
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WARN_ON_ONCE(kuap >> 16 != MD_APG_KUAP >> 16);
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WARN_ON_ONCE(mfspr(SPRN_MD_AP) >> 16 != MD_APG_KUAP >> 16);
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return kuap;
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return 0;
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}
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static inline void __allow_user_access(void __user *to, const void __user *from,
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@ -58,12 +58,10 @@ static inline void __kuap_kernel_restore(struct pt_regs *regs, unsigned long kua
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static inline unsigned long __kuap_get_and_assert_locked(void)
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{
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unsigned long kuap = mfspr(SPRN_PID);
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if (IS_ENABLED(CONFIG_PPC_KUAP_DEBUG))
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WARN_ON_ONCE(kuap);
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WARN_ON_ONCE(mfspr(SPRN_PID));
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return kuap;
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return 0;
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}
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static inline void __allow_user_access(void __user *to, const void __user *from,
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