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[2001:1ae9:1c2:4c00:726e:c10f:8833:ff22]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-57d27198948sm45831a12.54.2024.06.20.02.06.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Jun 2024 02:06:31 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 20 Jun 2024 11:06:29 +0200 To: Oleg Nesterov Cc: "Liao, Chang" , rostedt@goodmis.org, mhiramat@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, nathan@kernel.org, peterz@infradead.org, mingo@redhat.com, mark.rutland@arm.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH bpf-next] uprobes: Fix the xol slots reserved for uretprobe trampoline Message-ID: References: <20240619013411.756995-1-liaochang1@huawei.com> <20240619143852.GA24240@redhat.com> <7cfa9f1f-d9ce-b6bb-3fe0-687fae9c77c4@huawei.com> <20240620083602.GB30070@redhat.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240620083602.GB30070@redhat.com> On Thu, Jun 20, 2024 at 10:36:02AM +0200, Oleg Nesterov wrote: > On 06/20, Liao, Chang wrote: > > > > However, when i asm porting uretprobe trampoline to arm64 > > to explore its benefits on that architecture, i discovered the problem that > > single slot is not large enought for trampoline code. ah ok, makes sense now.. x86_64 has the slot big enough for the trampoline, but arm64 does not > > Ah, but then I'd suggest to make the changelog more clear. It looks as > if the problem was introduced by the patch from Jiri. Note that we was > confused as well ;) > > And, > > + /* Reserve enough slots for the uretprobe trampoline */ > + for (slot_nr = 0; > + slot_nr < max((insns_size / UPROBE_XOL_SLOT_BYTES), 1); > + slot_nr++) > > this doesn't look right. Just suppose that insns_size = UPROBE_XOL_SLOT_BYTES + 1. > I'd suggest DIV_ROUND_UP(insns_size, UPROBE_XOL_SLOT_BYTES). > > And perhaps it would be better to send this change along with > uretprobe_trampoline_for_arm64 ? +1, also I'm curious what's the gain on arm64? thanks, jirka