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

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Message-ID: <20240710131732.GA14582@willie-the-truck>
Date: Wed, 10 Jul 2024 14:17:33 +0100
From: Will Deacon <will@...nel.org>
To: Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Joey Gouly <joey.gouly@....com>,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: 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@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Steven Price <steven.price@....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@...nel.org>

Will