linux-kernel - Re: [PATCH v2 09/21] x86/virt/tdx: Get information about TDX module and convertible memory

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Date:   Mon, 28 Mar 2022 13:22:25 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     Isaku Yamahata <isaku.yamahata@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        dave.hansen@...el.com, seanjc@...gle.com, pbonzini@...hat.com,
        kirill.shutemov@...ux.intel.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, peterz@...radead.org,
        tony.luck@...el.com, ak@...ux.intel.com, dan.j.williams@...el.com,
        isaku.yamahata@...el.com
Subject: Re: [PATCH v2 09/21] x86/virt/tdx: Get information about TDX module
 and convertible memory

On Mon, Mar 28, 2022 at 02:30:05PM +1300,
Kai Huang <kai.huang@...el.com> wrote:

> 
> > > +
> > > +static int sanitize_cmrs(struct cmr_info *cmr_array, int cmr_num)
> > > +{
> > > +	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;
> > > +
> > > +		/* 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;
> > > +		}
> > > +	}
> > > +
> > > +	/*
> > > +	 * Also a sane BIOS should never generate invalid CMR(s) between
> > > +	 * two valid CMRs.  Sanity check this and simply return error in
> > > +	 * this case.
> > > +	 */
> > > +	for (j = i; j < cmr_num; j++)
> > > +		if (cmr_valid(&cmr_array[j])) {
> > > +			pr_err("Firmware bug: invalid CMR(s) among valid CMRs.\n");
> > > +			return -EFAULT;
> > > +		}
> > 
> > This check doesn't make sense because above i-for loop has break.
> 
> The break in above i-for loop will hit at the first invalid CMR entry.  Yes "j =
> i" will make double check on this invalid CMR entry, but it should have no
> problem.  Or we can change to "j = i + 1" to skip the first invalid CMR entry.
> 
> Does this make sense?

It makes sense. Somehow I missed j = i. I scratch my review.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>