Re: [PATCH v11 12/20] x86/virt/tdx: Allocate and set up PAMTs for TDMRs

[Dave Hansen]

On 6/8/23 16:24, kirill.shutemov@xxxxxxxxxxxxxxx wrote:
>>  	ret = -EINVAL;
>> +	if (ret)
>> +		tdmrs_free_pamt_all(&tdx_tdmr_list);
>> +	else
>> +		pr_info("%lu KBs allocated for PAMT.\n",
>> +				tdmrs_count_pamt_pages(&tdx_tdmr_list) * 4);
> "* 4"? This is very cryptic. procfs uses "<< (PAGE_SHIFT - 10)" which
> slightly less magic to me. And just make the helper that returns kilobytes
> to begin with, if it is the only caller.

Let's look at where this data comes from:

+static unsigned long tdmrs_count_pamt_pages(struct tdmr_info_list
*tdmr_list)
+{
+	unsigned long pamt_npages = 0;
+	int i;
+
+	for (i = 0; i < tdmr_list->nr_consumed_tdmrs; i++) {
+		unsigned long pfn, npages;
+
+		tdmr_get_pamt(tdmr_entry(tdmr_list, i), &pfn, &npages);
+		pamt_npages += npages;
+	}

OK, so tdmr_get_pamt() is getting it in pages.  How is it *stored*?

+static void tdmr_get_pamt(struct tdmr_info *tdmr, unsigned long *pamt_pfn,
+			  unsigned long *pamt_npages)
+{
...
+	pamt_sz = tdmr->pamt_4k_size + tdmr->pamt_2m_size + tdmr->pamt_1g_size;
++	*pamt_pfn = PHYS_PFN(pamt_base);
+	*pamt_npages = pamt_sz >> PAGE_SHIFT;
+}

Oh, it's actually stored in bytes.  So to print it out you actually
convert it from bytes->pages->kbytes.  Not the best.

If tdmr_get_pamt() just returned 'pamt_size_bytes', you could do one
conversion at:

	free_contig_range(pamt_pfn, pamt_size_bytes >> PAGE_SIZE);

and since tdmrs_count_pamt_pages() has only one caller you can just make
it:  tdmrs_count_pamt_kb().  The print becomes:

	pr_info("%lu KBs allocated for PAMT.\n",
		tdmrs_count_pamt_kb(&tdx_tdmr_list) * 4);

and tdmrs_count_pamt_kb() does something super fancy like:

	return pamt_size_bytes / 1024;

which makes total complete obvious sense and needs zero explanation.