Re: [PATCH v5 02/10] irqchip/gic-v3-its: Align shared ITS allocations to the CoCo shared granule size

[Marc Zyngier <maz@kernel.org>]

On Mon, 06 Jul 2026 07:04:24 +0100,
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org> wrote:
> 
> ITS tables allocated by the coco guest are shared with the hypervisor.
> These allocations must satisfy the host shared-buffer granule size so that
> the full converted range is safe for host access.
> 
> Allocate ITS pages using a size rounded up to the shared granule size and
> use the same allocation order when encrypting, decrypting and freeing the
> memory. Also grow the ITT cache in shared-granule sized chunks instead of
> assuming PAGE_SIZE is sufficient.
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index b57d81ad33a0..5d6d38aa0dae 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -213,16 +213,17 @@ static gfp_t gfp_flags_quirk;
>  static struct page *its_alloc_pages_node(int node, gfp_t gfp,
>  					 unsigned int order)
>  {
> +	unsigned int alloc_order;
>  	struct page *page;
>  	int ret = 0;
>  
> -	page = alloc_pages_node(node, gfp | gfp_flags_quirk, order);
> -
> +	alloc_order = get_order(mem_cc_align_to_shared_granule(PAGE_SIZE << order));
> +	page = alloc_pages_node(node, gfp | gfp_flags_quirk, alloc_order);
>  	if (!page)
>  		return NULL;
>  
>  	ret = set_memory_decrypted((unsigned long)page_address(page),
> -				   1 << order);
> +				   1 << alloc_order);
>  	/*
>  	 * If set_memory_decrypted() fails then we don't know what state the
>  	 * page is in, so we can't free it. Instead we leak it.
> @@ -241,13 +242,16 @@ static struct page *its_alloc_pages(gfp_t gfp, unsigned int order)
>  
>  static void its_free_pages(void *addr, unsigned int order)
>  {
> +	int alloc_order;
> +
> +	alloc_order = get_order(mem_cc_align_to_shared_granule(PAGE_SIZE << order));
>  	/*
>  	 * If the memory cannot be encrypted again then we must leak the pages.
>  	 * set_memory_encrypted() will already have WARNed.
>  	 */
> -	if (set_memory_encrypted((unsigned long)addr, 1 << order))
> +	if (set_memory_encrypted((unsigned long)addr, 1 << alloc_order))
>  		return;
> -	free_pages((unsigned long)addr, order);
> +	free_pages((unsigned long)addr, alloc_order);

The comments I had in [1] are still applicable.

	M.

[1] https://lore.kernel.org/all/86zf2ozrb8.wl-maz@kernel.org/

-- 
Without deviation from the norm, progress is not possible.