Re: [PATCH v4 12/15] irqchip/gic-v3-its: Share ITS tables with a non-trusted hypervisor

On Mon, Jul 01, 2024 at 10:55:02AM +0100, Steven Price wrote:

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@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
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(-)

I gave this (and the following patch) a spin in a protected guest under
pKVM and was able to use MSIs for my virtio devices, so:

Tested-by: Will Deacon <will@kernel.org>

Will