linux-kernel - Re: [PATCH v3] x86/sgx: Do not consider unsanitized pages an error

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Date:   Thu, 25 Aug 2022 22:22:14 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linux-sgx@...r.kernel.org, Paul Menzel <pmenzel@...gen.mpg.de>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] x86/sgx: Do not consider unsanitized pages an error

On Thu, Aug 25, 2022 at 11:51:18AM -0700, Dave Hansen wrote:
> On 8/25/22 01:08, Jarkko Sakkinen wrote:
> > +	/* Can happen, when the initialization is retracted: */
> > +	if (verbose && dirty_count > 0)
> > +		pr_info("%d unsanitized pages\n", dirty_count);
> >  }
> >  
> >  static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page)
> > @@ -394,11 +403,8 @@ static int ksgxd(void *p)
> >  	 * 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);
> > -
> > -	/* sanity check: */
> > -	WARN_ON(!list_empty(&sgx_dirty_page_list));
> > +	__sgx_sanitize_pages(&sgx_dirty_page_list, false);
> > +	__sgx_sanitize_pages(&sgx_dirty_page_list, true);
> 
> This is backwards, IMNHO.
> 
> Make __sgx_sanitize_pages() return the number of pages that it leaves
> dirty.
> 
> 	__sgx_sanitize_pages(&sgx_dirty_page_list)
> 	left_dirty = __sgx_sanitize_pages(&sgx_dirty_page_list);
> 	if (left_dirty)
> 		pr_warn(...);

I like this and my patch has already the counter in place
so why not.

> That rids us of the mystery true/false and puts the pr_warn() in a place
> that makes logical sense.  Then, let's either *not* do the
> 
> 	pr_err_ratelimited(EREMOVE_ERROR_MESSAGE, ret, ret);
> 
> at all, or make it an unconditional pr_warn_ratelimited().  They're not
> going to be common and multiple messages are virtually worthless anyway.
> 
> I actually think a common tracepoint, or out-of-line ENCLS/ENCLU
> functions that can be easily ftraced are a much better idea than a
> one-off pr_whatever().

I like the tracepoint idea more than out-of-line ENCLS/ENCLU
because out-of-line is more "intrusive" change to the code
semantics than a tracepoint.

BR, Jarkko