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Date:   Mon, 5 Sep 2022 13:17:32 +0300
From:   "jarkko@kernel.org" <jarkko@kernel.org>
To:     "Huang, Kai" <kai.huang@intel.com>
Cc:     "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
        "pmenzel@molgen.mpg.de" <pmenzel@molgen.mpg.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "Dhanraj, Vijay" <vijay.dhanraj@intel.com>,
        "Chatre, Reinette" <reinette.chatre@intel.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "x86@kernel.org" <x86@kernel.org>,
        "haitao.huang@linux.intel.com" <haitao.huang@linux.intel.com>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] x86/sgx: Do not fail on incomplete sanitization on
 premature stop of ksgxd
Message-ID: <YxXMvPLfxdv8QlJo@kernel.org>
References: <20220903060108.1709739-1-jarkko@kernel.org>
 <20220903060108.1709739-2-jarkko@kernel.org>
 <YxMr7hIXsNcWAiN5@kernel.org>
 <a5fa56bdc57d6472a306bd8d795afc674b724538.camel@intel.com>
 <YxXFGLSmRri2T1yb@kernel.org>
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On Mon, Sep 05, 2022 at 12:44:56PM +0300, jarkko@kernel.org wrote:
> On Mon, Sep 05, 2022 at 07:50:33AM +0000, Huang, Kai wrote:
> > On Sat, 2022-09-03 at 13:26 +0300, Jarkko Sakkinen wrote:
> > > > ? static int ksgxd(void *p)
> > > > ? {
> > > > +	unsigned long left_dirty;
> > > > +
> > > > ??	set_freezable();
> > > > ? 
> > > > ??	/*
> > > > ??	 * Sanitize pages in order to recover from kexec(). The 2nd pass is
> > > > ??	 * required for SECS pages, whose child pages blocked EREMOVE.
> > > > ??	 */
> > > > -	__sgx_sanitize_pages(&sgx_dirty_page_list);
> > > > -	__sgx_sanitize_pages(&sgx_dirty_page_list);
> > > > +	left_dirty = __sgx_sanitize_pages(&sgx_dirty_page_list);
> > > > +	pr_debug("%ld unsanitized pages\n", left_dirty);
> > > ????????????????? %lu
> > > 
> > 
> > I assume the intention is to print out the unsanitized SECS pages, but what is
> > the value of printing it? To me it doesn't provide any useful information, even
> > for debug.
> 
> How do you measure "useful"?
> 
> If for some reason there were unsanitized pages, I would at least
> want to know where it ended on the first value.
> 
> Plus it does zero harm unless you explicitly turn it on.

I would split it though for a separate patch because it does not need
to be part of the stable fix and change it to:

        if (left_dirty)
                pr_debug("%lu unsanitized pages\n", left_dirty);

BR, Jarkko