Re: [PATCH v2 12/14] arm64: realm: Support nonsecure ITS emulation shared

Steven Price
2024-05-23T09:57:43Z

On 22/05/2024 18:05, Catalin Marinas wrote:
> On Wed, May 22, 2024 at 04:52:45PM +0100, Steven Price wrote:
>> On 15/05/2024 12:01, Catalin Marinas wrote:
>>> On Fri, Apr 12, 2024 at 09:42:11AM +0100, Steven Price wrote:
>>>> @@ -3432,7 +3468,16 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>>>> nr_ites = max(2, nvecs);
>>>> sz = nr_ites * (FIELD_GET(GITS_TYPER_ITT_ENTRY_SIZE, its->typer) + 1);
>>>> sz = max(sz, ITS_ITT_ALIGN) + ITS_ITT_ALIGN - 1;
>>>> - itt = kzalloc_node(sz, GFP_KERNEL, its->numa_node);
>>>> + itt_order = get_order(sz);
>>>> + page = its_alloc_shared_pages_node(its->numa_node,
>>>> + GFP_KERNEL | __GFP_ZERO,
>>>> + itt_order);
>>>
>>> How much do we waste by going for a full page always if this is going to
>>> be used on the host?
>>
>> sz is a minimum of ITS_ITT_ALIGN*2-1 - which is 511 bytes. So
>> potentially PAGE_SIZE-512 bytes could be wasted here (minus kmalloc
>> overhead).
>
> That I figured out as well but how many times is this path called with a
> size smaller than a page?
>

That presumably depends on the number of devices in the guest. For my
test guest setup (using kvmtool) this is called 3 times each with sz=511.

Steve