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Tue, 27 Jul 2021 05:38:16 -0700 (PDT) Received: from [192.168.1.136] ([79.116.5.179]) by smtp.gmail.com with ESMTPSA id w9sm2939077wmc.19.2021.07.27.05.38.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jul 2021 05:38:16 -0700 (PDT) Message-ID: Subject: Re: [patch 1/4] add basic task isolation prctl interface From: nsaenzju@redhat.com To: Marcelo Tosatti Cc: linux-kernel@vger.kernel.org, Nitesh Lal , Frederic Weisbecker , Christoph Lameter , Juri Lelli , Peter Zijlstra , Alex Belits , Peter Xu Date: Tue, 27 Jul 2021 14:38:15 +0200 In-Reply-To: <20210727110050.GA502360@fuller.cnet> References: <20210727103803.464432924@fuller.cnet> <20210727104119.551607458@fuller.cnet> <7b2d6bf91d30c007e19a7d2cbddcb2460e72d163.camel@redhat.com> <20210727110050.GA502360@fuller.cnet> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.40.3 (3.40.3-1.fc34) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Marcelo, On Tue, 2021-07-27 at 08:00 -0300, Marcelo Tosatti wrote: > On Tue, Jul 27, 2021 at 12:48:33PM +0200, nsaenzju@redhat.com wrote: > > On Tue, 2021-07-27 at 07:38 -0300, Marcelo Tosatti wrote: > > > +Isolation mode (PR_ISOL_MODE): > > > +------------------------------ > > > + > > > +- PR_ISOL_MODE_NONE (arg4): no per-task isolation (default mode). > > > + PR_ISOL_EXIT sets mode to PR_ISOL_MODE_NONE. > > > + > > > +- PR_ISOL_MODE_NORMAL (arg4): applications can perform system calls normally, > > > + and in case of interruption events, the notifications can be collected > > > + by BPF programs. > > > + In this mode, if system calls are performed, deferred actions initiated > > > + by the system call will be executed before return to userspace. > > > + > > > +Other modes, which for example send signals upon interruptions events, > > > +can be implemented. > > > > Shouldn't this be a set of flags that enable specific isolation features? > > Something the likes of 'PR_ISOL_QUIESCE_ON_EXIT'. Modes seem more restrictive > > and too much of a commitment. If we merge MODE_NORMAL as is, we won't be able > > to tweak/extend its behaviour in the future. > > Hi Nicolas, > > Well, its assuming PR_ISOL_MODE_NORMAL means "enable all isolation > features on return to userspace". > > Later on, if desired, can add extend interface as follows (using > Christoph's idea to not perform automatic quiesce on return to > userspace, but expose which parts need quiescing > so userspace can do it on its own, as an example): > > #define PR_ISOL_QUIESCE_ON_EXIT (1<<0) > #define PR_ISOL_VSYSCALL_PAGE (1<<1) > ... > > unsigned long bitmap = PR_ISOL_VSYSCALL_PAGE; > > /* allow system calls */ > prctl(PR_ISOL_SET, PR_ISOL_MODE, PR_ISOL_MODE_NORMAL, 0, 0, 0); > > /* > * disable quiescing on exit, enable reporting through > * vsyscall page > */ > prctl(PR_ISOL_SET, PR_ISOL_FEATURES, &bitmap, 0, 0); > /* > * configure vsyscall page > */ > prctl(PR_ISOL_VSYSCALLS, params, ...); > > So unless i am missing something, it is possible to tweak/extend the > interface. No? OK, sorry if I'm being thick, but what is the benefit of having a distincnt PR_ISOL_MODE instead expressing everything as PR_ISOL_FEATURES. PR_ISOL_MODE_NONE == Empty PR_ISOL_FEATURES bitmap PR_ISOL_MODE_NORMAL == Bitmap of commonly used PR_ISOL_FEATURES (we could introduce a define) PR_ISOL_MODE_NORMAL+PR_ISOL_VSYSCALLS == Custom bitmap Other than that, my rationale is that if you extend PR_ISOL_MODE_NORMAL's behaviour as new features are merged, wouldn't you be potentially breaking userspace (i.e. older applications might not like the new default)? -- Nicolás Sáenz