linux-kernel - Re: [PATCH v2 12/14] arm64: realm: Support nonsecure ITS emulation shared

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Date: Wed, 15 May 2024 12:01:01 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...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 v2 12/14] arm64: realm: Support nonsecure ITS emulation
 shared

On Fri, Apr 12, 2024 at 09:42:11AM +0100, Steven Price wrote:
> @@ -198,6 +201,33 @@ static DEFINE_IDA(its_vpeid_ida);
>  #define gic_data_rdist_rd_base()	(gic_data_rdist()->rd_base)
>  #define gic_data_rdist_vlpi_base()	(gic_data_rdist_rd_base() + SZ_128K)
>  
> +static struct page *its_alloc_shared_pages_node(int node, gfp_t gfp,
> +						unsigned int order)
> +{
> +	struct page *page;
> +
> +	if (node == NUMA_NO_NODE)
> +		page = alloc_pages(gfp, order);
> +	else
> +		page = alloc_pages_node(node, gfp, order);

I think you can just call alloc_pages_node() in both cases. This
function takes care of the NUMA_NO_NODE case itself.

> +
> +	if (page)
> +		set_memory_decrypted((unsigned long)page_address(page),
> +				     1 << order);
> +	return page;
> +}
> +
> +static struct page *its_alloc_shared_pages(gfp_t gfp, unsigned int order)
> +{
> +	return its_alloc_shared_pages_node(NUMA_NO_NODE, gfp, order);
> +}
> +
> +static void its_free_shared_pages(void *addr, unsigned int order)
> +{
> +	set_memory_encrypted((unsigned long)addr, 1 << order);
> +	free_pages((unsigned long)addr, order);
> +}

More of a nitpick on the naming: Are these functions used by the host as
well? The 'shared' part of the name does not make much sense, so maybe
just call them its_alloc_page() etc.

> @@ -3432,7 +3468,16 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>  	nr_ites = max(2, nvecs);
>  	sz = nr_ites * (FIELD_GET(GITS_TYPER_ITT_ENTRY_SIZE, its->typer) + 1);
>  	sz = max(sz, ITS_ITT_ALIGN) + ITS_ITT_ALIGN - 1;
> -	itt = kzalloc_node(sz, GFP_KERNEL, its->numa_node);
> +	itt_order = get_order(sz);
> +	page = its_alloc_shared_pages_node(its->numa_node,
> +					   GFP_KERNEL | __GFP_ZERO,
> +					   itt_order);

How much do we waste by going for a full page always if this is going to
be used on the host?

> +	if (!page)
> +		return NULL;
> +	itt = (void *)page_address(page);

page_address() has the void * type already.

-- 
Catalin