From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Christophe Leroy" <christophe.leroy@csgroup.eu>,
"Michael Ellerman" <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] powerpc/kuap: Avoid useless jump_label on empty function
Date: Tue, 06 Jun 2023 19:12:08 +1000 [thread overview]
Message-ID: <CT5G9KKH2R25.3QSRZU8EQXUZU@wheely> (raw)
In-Reply-To: <c2c9660cc4441dc37c477ce5cf60707c971bd2a1.1685963081.git.christophe.leroy@csgroup.eu>
On Mon Jun 5, 2023 at 9:04 PM AEST, Christophe Leroy wrote:
> Disassembly of interrupt_enter_prepare() shows a pointless nop before the mftb
>
> c000abf0 <interrupt_enter_prepare>:
> c000abf0: 81 23 00 84 lwz r9,132(r3)
> c000abf4: 71 29 40 00 andi. r9,r9,16384
> c000abf8: 41 82 00 28 beq- c000ac20 <interrupt_enter_prepare+0x30>
> c000abfc: ===> 60 00 00 00 nop <====
> c000ac00: 7d 0c 42 e6 mftb r8
> c000ac04: 80 e2 00 08 lwz r7,8(r2)
> c000ac08: 81 22 00 28 lwz r9,40(r2)
> c000ac0c: 91 02 00 24 stw r8,36(r2)
> c000ac10: 7d 29 38 50 subf r9,r9,r7
> c000ac14: 7d 29 42 14 add r9,r9,r8
> c000ac18: 91 22 00 08 stw r9,8(r2)
> c000ac1c: 4e 80 00 20 blr
> c000ac20: 60 00 00 00 nop
> c000ac24: 7d 5a c2 a6 mfmd_ap r10
> c000ac28: 3d 20 de 00 lis r9,-8704
> c000ac2c: 91 43 00 b0 stw r10,176(r3)
> c000ac30: 7d 3a c3 a6 mtspr 794,r9
> c000ac34: 4e 80 00 20 blr
>
> That comes from the call to kuap_loc(), allthough __kuap_lock() is an empty
> function on the 8xx.
>
> To avoid that, only perform kuap_is_disabled() check when there is something
> to do with __kuap_lock().
>
> Do the same with __kuap_save_and_lock() and __kuap_get_and_assert_locked().
Too bad static branch nops can't be eliminated.
> diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h
> index 54cf46808157..1b0215ff3710 100644
> --- a/arch/powerpc/include/asm/book3s/64/kup.h
> +++ b/arch/powerpc/include/asm/book3s/64/kup.h
> @@ -297,15 +297,7 @@ static inline unsigned long __kuap_get_and_assert_locked(void)
> WARN_ON_ONCE(amr != AMR_KUAP_BLOCKED);
> return amr;
> }
> -
> -/* Do nothing, book3s/64 does that in ASM */
> -static inline void __kuap_lock(void)
> -{
> -}
> -
> -static inline void __kuap_save_and_lock(struct pt_regs *regs)
> -{
> -}
> +#define __kuap_get_and_assert_locked __kuap_get_and_assert_locked
Maybe leave in /* __kuap_lock notrequired, book3s/64 does that in ASM */
? Seems okay though
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Thanks,
Nick
next prev parent reply other threads:[~2023-06-06 9:13 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-05 11:04 [PATCH 1/4] powerpc/kuap: Avoid unnecessary reads of MD_AP Christophe Leroy
2023-06-05 11:04 ` [PATCH 2/4] powerpc/kuap: Avoid useless jump_label on empty function Christophe Leroy
2023-06-06 9:12 ` Nicholas Piggin [this message]
2023-06-05 11:04 ` [PATCH 3/4] powerpc/kuap: Refactor static branch for disabling kuap Christophe Leroy
2023-06-06 9:16 ` Nicholas Piggin
2023-06-22 6:08 ` Christophe Leroy
2023-06-05 11:04 ` [PATCH 4/4] powerpc/kuap: Make disabling KUAP at boottime optional Christophe Leroy
2023-06-06 9:27 ` Nicholas Piggin
2023-06-22 6:20 ` Christophe Leroy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CT5G9KKH2R25.3QSRZU8EQXUZU@wheely \
--to=npiggin@gmail.com \
--cc=christophe.leroy@csgroup.eu \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mpe@ellerman.id.au \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).