linux-kernel - RE: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map when adding it to RMP table

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Date:   Mon, 1 Aug 2022 23:57:09 +0000
From:   "Kalra, Ashish" <Ashish.Kalra@....com>
To:     Borislav Petkov <bp@...en8.de>
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Subject: RE: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map
 when adding it to RMP table

[AMD Official Use Only - General]

Hello Boris,

>> Subject: x86/sev: Invalid pages from direct map when adding it to RMP 
>> table

>"...: Invalidate pages from the direct map when adding them to the RMP table"
Ok

>> +static int restore_direct_map(u64 pfn, int npages) {
>> +	int i, ret = 0;
>> +
>> +	for (i = 0; i < npages; i++) {
>> +		ret = set_direct_map_default_noflush(pfn_to_page(pfn + i));

>set_memory_p() ?

You mean set_memory_present() ? 

Is there an issue with not using set_direct_map_default_noflush(), it is easier to correlate with
this function and it's functionality of restoring the page in the kernel direct map ?

> +		if (ret)
> +			goto cleanup;
> +	}
> +
> +cleanup:
> +	WARN(ret > 0, "Failed to restore direct map for pfn 0x%llx\n", pfn + 
> +i);

>Warn for each pfn?!

>That'll flood dmesg mightily.

> +	return ret;
> +}
> +
> +static int invalid_direct_map(unsigned long pfn, int npages) {
> +	int i, ret = 0;
> +
> +	for (i = 0; i < npages; i++) {
> +		ret = set_direct_map_invalid_noflush(pfn_to_page(pfn + i));

>As above, set_memory_np() doesn't work here instead of looping over each page?

Yes, set_memory_np() looks more efficient to use instead of looping over each page.

But again, calling set_direct_map_invalid_noflush() is easier to understand from the
calling function's point of view as it correlates to the functionality of invalidating the 
page from kernel direct map ? 

>> +	if (val->assigned) {
>> +		if (invalid_direct_map(pfn, npages)) {
>. +			pr_err("Failed to unmap pfn 0x%llx pages %d from direct_map\n",

>"Failed to unmap %d pages at pfn 0x... from the direct map\n"
Ok.

>> +	if (!ret && !val->assigned) {
>> +		if (restore_direct_map(pfn, npages)) {
>> +			pr_err("Failed to map pfn 0x%llx pages %d in direct_map\n",

>"Failed to map %d pages at pfn 0x... into the direct map\n"
Ok.

Thanks,
Ashish