[U-Boot] [PATCH 2/9] arm64: Make full va map code more dynamic

[Stephen Warren]

On 02/22/2016 11:37 AM, Alexander Graf wrote:
>
> On Feb 22, 2016, at 7:18 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>
>> On 02/21/2016 06:57 PM, Alexander Graf wrote:
>>> The idea to generate our pages tables from an array of memory ranges
>>> is very sound. However, instead of hard coding the code to create up
>>> to 2 levels of 64k granule page tables, we really should just create
>>> normal 4k page tables that allow us to set caching attributes on 2M
>>> or 4k level later on.
>>>
>>> So this patch moves the full_va mapping code to 4k page size and
>>> makes it fully flexible to dynamically create as many levels as
>>> necessary for a map (including dynamic 1G/2M pages). It also adds
>>> support to dynamically split a large map into smaller ones when
>>> some code wants to set dcache attributes.
>>>
>>> With all this in place, there is very little reason to create your
>>> own page tables in board specific files.
>>
>>> diff --git a/arch/arm/cpu/armv8/cache_v8.c b/arch/arm/cpu/armv8/cache_v8.c
>>
>>> +/* Creates a new full table (512 entries) and sets *pte to refer to it */
>>> +static u64 *create_table(void)
>>
>> I think that comment is stale (there's no *pte; I assume it should say "returns").
>
> Oops, yes. I split the pte setting into a separate function and forgot to update the comment. Nice catch.
>
>>
>>> +/* Returns the estimated required size of all page tables */
>>> +u64 get_page_table_size(void)
>>> +{
>>> +	int i;
>>> +	u64 one_pt = MAX_PTE_ENTRIES * sizeof(u64);
>>> +	u64 size = 0;
>>> +
>>> +	/* root page table */
>>> +	size += one_pt;
>>
>> Isn't the root page table level 0? So, that accounts for the page table that's indexed by VA bits 47:39.
>
> Yes, or - if your va_bits < 39 it actually accounts for level 1 because the page table starts at Lv1.
>
>>
>>> +	for (i = 0; i < ARRAY_SIZE(mem_map); i++) {
>>> +		struct mm_region *map = &mem_map[i];
>>> +
>>> +		/* Account for Lv0 page tables */
>>> +		size += one_pt * ((map->size >> 39) + 1);
>>
>> So here, isn't the code accounting for level 1 tables, not level 0 tables? That is, the tables indexed by VA bits 38:30.
>>
>> (As an aside for myself when I come back and read this later, the shift is 39, since we need to allocate as many tables as there are values for bits 39 and above).
>
> I definitely should use the level2shift helper here, yes.
>
>>
>>> +		/* 1GB aligned pages fit already, so count the others */
>>> +		if (map->size & 0x3fffffffULL)
>>> +			size += one_pt;
>>> +		if (map->base & 0x3fffffffULL)
>>> +			size += one_pt;
>>
>> Here, I believe we're accounting for any required level 2 tables (which are indexed by VA bits 29:21).
>>
>> We seem to be missing code inside the loop that accounts for any required level 3 tables (indexed by VA bits 20:12).
>
> The reason I didn't account for level 3 is that *usually* we shouldn't have those around. I guess the size estimation really could use some more thought...

As you mention, it's unlikely we'd need level 3 in practice.

However, we should still either account for it now, or explicitly fail 
if the code for that isn't written yet. I'd like at least an 
assert()/panic()/... somewhere (here seems best?) if the mem_map[] 
entries are not 2MB-aligned.