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

[Marc Zyngier <maz@kernel.org>]

On Mon, 19 Aug 2024 15:51:00 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> Hi Steven,
> 
> On 19/08/2024 14:19, 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.
> > 
> 
> This may not be sufficient to make it future proof. We need to detect if
> the GIC is private vs shared, before we make the allocation
> choice. Please see below :

What do you mean by that? Do you foresee a *GICv3* implementation on
the realm side?

[...]

> How about something like this folded into this patch ? Or if this
> patch goes in independently, we could carry the following as part of
> the CCA
> series.
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c
> b/drivers/irqchip/irq-gic-v3-its.c
> index 6f4ddf7faed1..f1a779b52210 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -209,7 +209,7 @@ static struct page *its_alloc_pages_node(int node,
> gfp_t gfp,
> 
>  	page = alloc_pages_node(node, gfp, order);
> 
> -	if (page)
> +	if (gic_rdists->is_shared && page)
>  		set_memory_decrypted((unsigned long)page_address(page),
>  				     BIT(order));
>  	return page;
> @@ -222,7 +222,8 @@ static struct page *its_alloc_pages(gfp_t gfp,
> unsigned int order)
> 
>  static void its_free_pages(void *addr, unsigned int order)
>  {
> -	set_memory_encrypted((unsigned long)addr, BIT(order));
> +	if (gic_rdists->is_shared)
> +		set_memory_encrypted((unsigned long)addr, BIT(order));
>  	free_pages((unsigned long)addr, order);
>  }
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 6fb276504bcc..48c6b2c8dd8c 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -2015,6 +2015,8 @@ static int __init gic_init_bases(phys_addr_t
> dist_phys_base,
>  	typer = readl_relaxed(gic_data.dist_base + GICD_TYPER);
>  	gic_data.rdists.gicd_typer = typer;
> 
> +	gic_data.rdists.is_shared =
> !arm64_is_iomem_private(gic_data.dist_phys_base,
> +							    PAGE_SIZE);

Why would you base the status of the RDs on that of the distributor?

>  	gic_enable_quirks(readl_relaxed(gic_data.dist_base + GICD_IIDR),
>  			  gic_quirks, &gic_data);
> 
> diff --git a/include/linux/irqchip/arm-gic-v3.h
> b/include/linux/irqchip/arm-gic-v3.h
> index 728691365464..1edc33608d52 100644
> --- a/include/linux/irqchip/arm-gic-v3.h
> +++ b/include/linux/irqchip/arm-gic-v3.h
> @@ -631,6 +631,7 @@ struct rdists {
>  	bool			has_rvpeid;
>  	bool			has_direct_lpi;
>  	bool			has_vpend_valid_dirty;
> +	bool			is_shared;
>  };
> 
>  struct irq_domain;
> 

I really don't like this.

If we have to go down the route of identifying whether the GIC needs
encryption or not based on the platform, then maybe we should bite the
bullet and treat it as a first class device, given that we expect
devices to be either realm or non-secure.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.