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

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Date:   Thu, 25 Aug 2022 11:51:18 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, linux-sgx@...r.kernel.org
Cc:     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 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(...);

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().