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Fri, 13 Jun 2025 16:41:34 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id zUAIGr5UTGhiPgAAD6G6ig (envelope-from ); Fri, 13 Jun 2025 16:41:34 +0000 Date: Fri, 13 Jun 2025 18:41:34 +0200 Message-ID: <87msabr3up.wl-tiwai@suse.de> From: Takashi Iwai To: Christophe Leroy Cc: Jaroslav Kysela , Takashi Iwai , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-sound@vger.kernel.org, Herve Codina Subject: Re: [PATCH v2 2/4] ALSA: pcm: Convert SNDRV_PCM_IOCTL_SYNC_PTR to user_access_begin/user_access_end() In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spamd-Result: default: False [-3.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[7]; RCVD_TLS_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; TO_DN_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid] X-Spam-Level: X-Spam-Flag: NO X-Spam-Score: -3.30 On Fri, 13 Jun 2025 17:37:09 +0200, Christophe Leroy wrote: > > With user access protection (Called SMAP on x86 or KUAP on powerpc) > each and every call to get_user() or put_user() performs heavy > operations to unlock and lock kernel access to userspace. > > SNDRV_PCM_IOCTL_SYNC_PTR is a hot path which is called really often > and needs to run as fast as possible. > > To improve performance, perform user accesses by blocks using > user_access_begin/user_access_end() and unsafe_get_user()/ > unsafe_put_user(). > > Before the patch the 9 calls to put_user() at the end of > snd_pcm_ioctl_sync_ptr_compat() imply the following set of > instructions about 9 times (access_ok - enable user - write - disable > user): > 0.00 : c057f858: 3d 20 7f ff lis r9,32767 > 0.29 : c057f85c: 39 5e 00 14 addi r10,r30,20 > 0.77 : c057f860: 61 29 ff fc ori r9,r9,65532 > 0.32 : c057f864: 7c 0a 48 40 cmplw r10,r9 > 0.36 : c057f868: 41 a1 fb 58 bgt c057f3c0 > 0.30 : c057f86c: 3d 20 dc 00 lis r9,-9216 > 1.95 : c057f870: 7d 3a c3 a6 mtspr 794,r9 > 0.33 : c057f874: 92 8a 00 00 stw r20,0(r10) > 0.27 : c057f878: 3d 20 de 00 lis r9,-8704 > 0.28 : c057f87c: 7d 3a c3 a6 mtspr 794,r9 > ... > > A perf profile shows that in total the 9 put_user() represent 36% of > the time spent in snd_pcm_ioctl() and about 80 instructions. > > With this patch everything is done in 13 instructions and represent > only 15% of the time spent in snd_pcm_ioctl(): > > 0.57 : c057f5dc: 3d 20 dc 00 lis r9,-9216 > 0.98 : c057f5e0: 7d 3a c3 a6 mtspr 794,r9 > 0.16 : c057f5e4: 92 7f 00 04 stw r19,4(r31) > 0.63 : c057f5e8: 93 df 00 0c stw r30,12(r31) > 0.16 : c057f5ec: 93 9f 00 10 stw r28,16(r31) > 4.95 : c057f5f0: 92 9f 00 14 stw r20,20(r31) > 0.19 : c057f5f4: 92 5f 00 18 stw r18,24(r31) > 0.49 : c057f5f8: 92 bf 00 1c stw r21,28(r31) > 0.27 : c057f5fc: 93 7f 00 20 stw r27,32(r31) > 5.88 : c057f600: 93 36 00 00 stw r25,0(r22) > 0.11 : c057f604: 93 17 00 00 stw r24,0(r23) > 0.00 : c057f608: 3d 20 de 00 lis r9,-8704 > 0.79 : c057f60c: 7d 3a c3 a6 mtspr 794,r9 > > Note that here the access_ok() in user_write_access_begin() is skipped > because the exact same verification has already been performed at the > beginning of the fonction with the call to user_read_access_begin(). > > Signed-off-by: Christophe Leroy Hm, with this patch, I got a compile warning: sound/core/snd-pcm.o: warning: objtool: .altinstr_replacement+0x12: redundant UACCESS disable It's with gcc-13.3.1. Takashi > --- > sound/core/pcm_native.c | 42 +++++++++++++++++++++++++---------------- > 1 file changed, 26 insertions(+), 16 deletions(-) > > diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c > index 20326aa377b0..fd69eea935b2 100644 > --- a/sound/core/pcm_native.c > +++ b/sound/core/pcm_native.c > @@ -3053,30 +3053,40 @@ static inline int snd_pcm_hwsync(struct snd_pcm_substream *substream) > } > > #define snd_pcm_sync_ptr_get_user(__f, __c, __ptr) ({ \ > - int __err = 0; \ > + __label__ failed; \ > + int __err = -EFAULT; \ > typeof(*(__ptr)) __user *__src = (__ptr); \ > \ > - if (get_user(__f, &src->flags) || \ > - get_user(__c.appl_ptr, &__src->c.control.appl_ptr) || \ > - get_user(__c.avail_min, &__src->c.control.avail_min)) \ > - __err = -EFAULT; \ > + if (!user_read_access_begin(__src, sizeof(*__src))) \ > + goto failed; \ > + unsafe_get_user(__f, &__src->flags, failed); \ > + unsafe_get_user(__c.appl_ptr, &__src->c.control.appl_ptr, failed); \ > + unsafe_get_user(__c.avail_min, &__src->c.control.avail_min, failed); \ > + __err = 0; \ > +failed: \ > + user_read_access_end(); \ > __err; \ > }) > > #define snd_pcm_sync_ptr_put_user(__s, __c, __ptr) ({ \ > - int __err = 0; \ > + __label__ failed; \ > + int __err = -EFAULT; \ > typeof(*(__ptr)) __user *__src = (__ptr); \ > \ > - if (put_user(__s.state, &__src->s.status.state) || \ > - put_user(__s.hw_ptr, &__src->s.status.hw_ptr) || \ > - put_user(__s.tstamp.tv_sec, &__src->s.status.tstamp_sec) || \ > - put_user(__s.tstamp.tv_nsec, &__src->s.status.tstamp_nsec) || \ > - put_user(__s.suspended_state, &__src->s.status.suspended_state) || \ > - put_user(__s.audio_tstamp.tv_sec, &__src->s.status.audio_tstamp_sec) || \ > - put_user(__s.audio_tstamp.tv_nsec, &__src->s.status.audio_tstamp_nsec) || \ > - put_user(__c.appl_ptr, &__src->c.control.appl_ptr) || \ > - put_user(__c.avail_min, &__src->c.control.avail_min)) \ > - __err = -EFAULT; \ > + if (!user_write_access_begin(__src, sizeof(*__src))) \ > + goto failed; \ > + unsafe_put_user(__s.state, &__src->s.status.state, failed); \ > + unsafe_put_user(__s.hw_ptr, &__src->s.status.hw_ptr, failed); \ > + unsafe_put_user(__s.tstamp.tv_sec, &__src->s.status.tstamp_sec, failed);\ > + unsafe_put_user(__s.tstamp.tv_nsec, &__src->s.status.tstamp_nsec, failed); \ > + unsafe_put_user(__s.suspended_state, &__src->s.status.suspended_state, failed); \ > + unsafe_put_user(__s.audio_tstamp.tv_sec, &__src->s.status.audio_tstamp_sec, failed); \ > + unsafe_put_user(__s.audio_tstamp.tv_nsec, &__src->s.status.audio_tstamp_nsec, failed); \ > + unsafe_put_user(__c.appl_ptr, &__src->c.control.appl_ptr, failed); \ > + unsafe_put_user(__c.avail_min, &__src->c.control.avail_min, failed); \ > + __err = 0; \ > +failed: \ > + user_write_access_end(); \ > __err; \ > }) > > -- > 2.47.0 >