linux-kernel - Re: [PATCH v3 09/21] x86/virt/tdx: Get information about TDX module and convertible memory

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Message-ID: <7887db8b5108b8dc9bd35868db561badca060b51.camel@intel.com>
Date:   Tue, 26 Apr 2022 12:05:23 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, dave.hansen@...el.com,
        len.brown@...el.com, tony.luck@...el.com,
        rafael.j.wysocki@...el.com, reinette.chatre@...el.com,
        dan.j.williams@...el.com, peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com, isaku.yamahata@...el.com
Subject: Re: [PATCH v3 09/21] x86/virt/tdx: Get information about TDX module
 and convertible memory

> 
> > +}
> > +
> > +static int sanitize_cmrs(struct cmr_info *cmr_array, int cmr_num)
> 
> Since this function only deals with tdx_cmr_array, why pass it
> as argument?

I received comments to use cmr_num as argument and pass tdx_cmr_num to
sanitize_cmrs() and finalize it at the end of this function.  In this case I
think it's better to pass tdx_cmr_array as argument.  It also saves some typing
(tdx_cmr_array vs cmr_array) in sanitize_cmrs().

> 
> > +{
> > +	int i, j;
> > +
> > +	/*
> > +	 * Intel TDX module spec, 20.7.3 CMR_INFO:
> > +	 *
> > +	 *   TDH.SYS.INFO leaf function returns a MAX_CMRS (32) entry
> > +	 *   array of CMR_INFO entries. The CMRs are sorted from the
> > +	 *   lowest base address to the highest base address, and they
> > +	 *   are non-overlapping.
> > +	 *
> > +	 * This implies that BIOS may generate invalid empty entries
> > +	 * if total CMRs are less than 32.  Skip them manually.
> > +	 */
> > +	for (i = 0; i < cmr_num; i++) {
> > +		struct cmr_info *cmr = &cmr_array[i];
> > +		struct cmr_info *prev_cmr = NULL;
> 
> Why not keep declarations together at the top of the function?

Why? They are only used in this for-loop.

> 
> > +
> > +		/* Skip further invalid CMRs */
> > +		if (!cmr_valid(cmr))
> > +			break;
> > +
> > +		if (i > 0)
> > +			prev_cmr = &cmr_array[i - 1];
> > +
> > +		/*
> > +		 * It is a TDX firmware bug if CMRs are not
> > +		 * in address ascending order.
> > +		 */
> > +		if (prev_cmr && ((prev_cmr->base + prev_cmr->size) >
> > +					cmr->base)) {
> > +			pr_err("Firmware bug: CMRs not in address ascending order.\n");
> > +			return -EFAULT;
> > +		}
> 
> Since above condition is only true for i > 0 case, why not combine them
> together if (i > 0) {...}

It will make an additional ident for the above if() {} to check prev_cmr and
cmr.  I don't see it is better?

-- 
Thanks,
-Kai