Re: [PATCH v5 17/19] irqchip/gic-v3-its: Share ITS tables with a non-trusted hypervisor

[Shanker Donthineni]

Hi Steve,

On 8/19/24 08:19, Steven Price wrote:
> External email: Use caution opening links or attachments
>
>
> Within a realm guest the ITS is emulated by the host. This means the
> allocations must have been made available to the host by a call to
> set_memory_decrypted(). Introduce an allocation function which performs
> this extra call.
>
> For the ITT use a custom genpool-based allocator that calls
> set_memory_decrypted() for each page allocated, but then suballocates
> the size needed for each ITT. Note that there is no mechanism
> implemented to return pages from the genpool, but it is unlikely the
> peak number of devices will so much larger than the normal level - so
> this isn't expected to be an issue.
>
> Co-developed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Tested-by: Will Deacon <will@xxxxxxxxxx>
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
> Changes since v3:
>   * Use BIT() macro.
>   * Use a genpool based allocator in its_create_device() to avoid
>     allocating a full page.
>   * Fix subject to drop "realm" and use gic-v3-its.
>   * Add error handling to ITS alloc/free.
> Changes since v2:
>   * Drop 'shared' from the new its_xxx function names as they are used
>     for non-realm guests too.
>   * Don't handle the NUMA_NO_NODE case specially - alloc_pages_node()
>     should do the right thing.
>   * Drop a pointless (void *) cast.
> ---
>   drivers/irqchip/irq-gic-v3-its.c | 139 ++++++++++++++++++++++++++-----
>   1 file changed, 116 insertions(+), 23 deletions(-)
...
> +
> +static void *itt_alloc_pool(int node, int size)
> +{
> +       unsigned long addr;
> +       struct page *page;
> +
> +       if (size >= PAGE_SIZE) {
> +               page = its_alloc_pages_node(node,
> +                                           GFP_KERNEL | __GFP_ZERO,
> +                                           get_order(size));
> +
> +               return page_address(page);
> +       }
> +
> +       do {
> +               addr = gen_pool_alloc(itt_pool, size);
> +               if (addr)
> +                       break;
> +
> +               page = its_alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 1);


Two (2^1) pages are allocated here, but only one page is being added to the pool.
Is this a typo or intentional?

> +               if (!page)
> +                       break;
> +
> +               gen_pool_add(itt_pool, (unsigned long)page_address(page),
> +                            PAGE_SIZE, node);
> +       } while (!addr);
> +
> +       return (void *)addr;
> +}
> +
> +static void itt_free_pool(void *addr, int size)

-Shanker