Re: [PATCH] irqchip/gic-v3-its: Ensure nr_ites >= nr_lpis

Ard Biesheuvel
2018-03-19T07:28:41Z

On 19 March 2018 at 15:27, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> Commit 4f2c7583e33e upstream.
>
> When struct its_device instances are created, the nr_ites member
> will be set to a power of 2 that equals or exceeds the requested
> number of MSIs passed to the msi_prepare() callback. At the same
> time, the LPI map is allocated to be some multiple of 32 in size,
> where the allocated size may be less than the requested size
> depending on whether a contiguous range of sufficient size is
> available in the global LPI bitmap.
>
> This may result in the situation where the nr_ites < nr_lpis, and
> since nr_ites is what we program into the hardware when we map the
> device, the additional LPIs will be non-functional.
>
> For bog standard hardware, this does not really matter. However,
> in cases where ITS device IDs are shared between different PCIe
> devices, we may end up allocating these additional LPIs without
> taking into account that they don't actually work.
>
> So let's make nr_ites at least 32. This ensures that all allocated
> LPIs are 'live', and that its_alloc_device_irq() will fail when
> attempts are made to allocate MSIs beyond what was allocated in
> the first place.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> [maz: updated comment]
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> [ardb: trivial tweak of unrelated context]
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---

Please apply to v4.9

> drivers/irqchip/irq-gic-v3-its.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index acb9d250a905..ac15e5d5d9b2 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -684,7 +684,7 @@ static struct irq_chip its_irq_chip = {
> * This gives us (((1UL << id_bits) - 8192) >> 5) possible allocations.
> */
> #define IRQS_PER_CHUNK_SHIFT 5
> -#define IRQS_PER_CHUNK (1 << IRQS_PER_CHUNK_SHIFT)
> +#define IRQS_PER_CHUNK (1UL << IRQS_PER_CHUNK_SHIFT)
>
> static unsigned long *lpi_bitmap;
> static u32 lpi_chunks;
> @@ -1320,11 +1320,10 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>
> dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> /*
> - * At least one bit of EventID is being used, hence a minimum
> - * of two entries. No, the architecture doesn't let you
> - * express an ITT with a single entry.
> + * We allocate at least one chunk worth of LPIs bet device,
> + * and thus that many ITEs. The device may require less though.
> */
> - nr_ites = max(2UL, roundup_pow_of_two(nvecs));
> + nr_ites = max(IRQS_PER_CHUNK, roundup_pow_of_two(nvecs));
> sz = nr_ites * its->ite_size;
> sz = max(sz, ITS_ITT_ALIGN) + ITS_ITT_ALIGN - 1;
> itt = kzalloc(sz, GFP_KERNEL);
> --
> 2.11.0
>