Re: [PATCH v3 12/14] arm64: realm: Support nonsecure ITS emulation shared

[Steven Price]

Hi Marc,

On 05/06/2024 14:39, Marc Zyngier wrote:
> The subject line is... odd. I'd expect something like:
> 
> "irqchip/gic-v3-its: Share ITS tables with a non-trusted hypervisor"
> 
> because nothing here should be CCA specific.

Good point - that's a much better subject.

> On Wed, 05 Jun 2024 10:30:04 +0100,
> Steven Price <steven.price@xxxxxxx> 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.
> 
> This doesn't mention that this patch radically changes the allocation
> of some tables.

I guess that depends on your definition of radical, see below.

>>
>> Co-developed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>> Signed-off-by: Steven Price <steven.price@xxxxxxx>
>> ---
>> 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 | 90 ++++++++++++++++++++++++--------
>>  1 file changed, 67 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 40ebf1726393..ca72f830f4cc 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/irqdomain.h>
>>  #include <linux/list.h>
>>  #include <linux/log2.h>
>> +#include <linux/mem_encrypt.h>
>>  #include <linux/memblock.h>
>>  #include <linux/mm.h>
>>  #include <linux/msi.h>
>> @@ -27,6 +28,7 @@
>>  #include <linux/of_pci.h>
>>  #include <linux/of_platform.h>
>>  #include <linux/percpu.h>
>> +#include <linux/set_memory.h>
>>  #include <linux/slab.h>
>>  #include <linux/syscore_ops.h>
>>  
>> @@ -163,6 +165,7 @@ struct its_device {
>>  	struct its_node		*its;
>>  	struct event_lpi_map	event_map;
>>  	void			*itt;
>> +	u32			itt_order;
>>  	u32			nr_ites;
>>  	u32			device_id;
>>  	bool			shared;
>> @@ -198,6 +201,30 @@ 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_pages_node(int node, gfp_t gfp,
>> +					 unsigned int order)
>> +{
>> +	struct page *page;
>> +
>> +	page = alloc_pages_node(node, gfp, order);
>> +
>> +	if (page)
>> +		set_memory_decrypted((unsigned long)page_address(page),
>> +				     1 << order);
> 
> Please use BIT(order).

Sure.

>> +	return page;
>> +}
>> +
>> +static struct page *its_alloc_pages(gfp_t gfp, unsigned int order)
>> +{
>> +	return its_alloc_pages_node(NUMA_NO_NODE, gfp, order);
>> +}
>> +
>> +static void its_free_pages(void *addr, unsigned int order)
>> +{
>> +	set_memory_encrypted((unsigned long)addr, 1 << order);
>> +	free_pages((unsigned long)addr, order);
>> +}
>> +
>>  /*
>>   * Skip ITSs that have no vLPIs mapped, unless we're on GICv4.1, as we
>>   * always have vSGIs mapped.
>> @@ -2212,7 +2239,8 @@ static struct page *its_allocate_prop_table(gfp_t gfp_flags)
>>  {
>>  	struct page *prop_page;
>>  
>> -	prop_page = alloc_pages(gfp_flags, get_order(LPI_PROPBASE_SZ));
>> +	prop_page = its_alloc_pages(gfp_flags,
>> +				    get_order(LPI_PROPBASE_SZ));
>>  	if (!prop_page)
>>  		return NULL;
>>  
>> @@ -2223,8 +2251,8 @@ static struct page *its_allocate_prop_table(gfp_t gfp_flags)
>>  
>>  static void its_free_prop_table(struct page *prop_page)
>>  {
>> -	free_pages((unsigned long)page_address(prop_page),
>> -		   get_order(LPI_PROPBASE_SZ));
>> +	its_free_pages(page_address(prop_page),
>> +		       get_order(LPI_PROPBASE_SZ));
>>  }
>>  
>>  static bool gic_check_reserved_range(phys_addr_t addr, unsigned long size)
>> @@ -2346,7 +2374,8 @@ static int its_setup_baser(struct its_node *its, struct its_baser *baser,
>>  		order = get_order(GITS_BASER_PAGES_MAX * psz);
>>  	}
>>  
>> -	page = alloc_pages_node(its->numa_node, GFP_KERNEL | __GFP_ZERO, order);
>> +	page = its_alloc_pages_node(its->numa_node,
>> +				    GFP_KERNEL | __GFP_ZERO, order);
>>  	if (!page)
>>  		return -ENOMEM;
>>  
>> @@ -2359,7 +2388,7 @@ static int its_setup_baser(struct its_node *its, struct its_baser *baser,
>>  		/* 52bit PA is supported only when PageSize=64K */
>>  		if (psz != SZ_64K) {
>>  			pr_err("ITS: no 52bit PA support when psz=%d\n", psz);
>> -			free_pages((unsigned long)base, order);
>> +			its_free_pages(base, order);
>>  			return -ENXIO;
>>  		}
>>  
>> @@ -2415,7 +2444,7 @@ static int its_setup_baser(struct its_node *its, struct its_baser *baser,
>>  		pr_err("ITS@%pa: %s doesn't stick: %llx %llx\n",
>>  		       &its->phys_base, its_base_type_string[type],
>>  		       val, tmp);
>> -		free_pages((unsigned long)base, order);
>> +		its_free_pages(base, order);
>>  		return -ENXIO;
>>  	}
>>  
>> @@ -2554,8 +2583,8 @@ static void its_free_tables(struct its_node *its)
>>  
>>  	for (i = 0; i < GITS_BASER_NR_REGS; i++) {
>>  		if (its->tables[i].base) {
>> -			free_pages((unsigned long)its->tables[i].base,
>> -				   its->tables[i].order);
>> +			its_free_pages(its->tables[i].base,
>> +				       its->tables[i].order);
>>  			its->tables[i].base = NULL;
>>  		}
>>  	}
>> @@ -2821,7 +2850,8 @@ static bool allocate_vpe_l2_table(int cpu, u32 id)
>>  
>>  	/* Allocate memory for 2nd level table */
>>  	if (!table[idx]) {
>> -		page = alloc_pages(GFP_KERNEL | __GFP_ZERO, get_order(psz));
>> +		page = its_alloc_pages(GFP_KERNEL | __GFP_ZERO,
>> +				       get_order(psz));
>>  		if (!page)
>>  			return false;
>>  
>> @@ -2940,7 +2970,8 @@ static int allocate_vpe_l1_table(void)
>>  
>>  	pr_debug("np = %d, npg = %lld, psz = %d, epp = %d, esz = %d\n",
>>  		 np, npg, psz, epp, esz);
>> -	page = alloc_pages(GFP_ATOMIC | __GFP_ZERO, get_order(np * PAGE_SIZE));
>> +	page = its_alloc_pages(GFP_ATOMIC | __GFP_ZERO,
>> +			       get_order(np * PAGE_SIZE));
>>  	if (!page)
>>  		return -ENOMEM;
>>  
>> @@ -2986,8 +3017,8 @@ static struct page *its_allocate_pending_table(gfp_t gfp_flags)
>>  {
>>  	struct page *pend_page;
>>  
>> -	pend_page = alloc_pages(gfp_flags | __GFP_ZERO,
>> -				get_order(LPI_PENDBASE_SZ));
>> +	pend_page = its_alloc_pages(gfp_flags | __GFP_ZERO,
>> +				    get_order(LPI_PENDBASE_SZ));
>>  	if (!pend_page)
>>  		return NULL;
>>  
>> @@ -2999,7 +3030,7 @@ static struct page *its_allocate_pending_table(gfp_t gfp_flags)
>>  
>>  static void its_free_pending_table(struct page *pt)
>>  {
>> -	free_pages((unsigned long)page_address(pt), get_order(LPI_PENDBASE_SZ));
>> +	its_free_pages(page_address(pt), get_order(LPI_PENDBASE_SZ));
>>  }
>>  
>>  /*
>> @@ -3334,8 +3365,9 @@ static bool its_alloc_table_entry(struct its_node *its,
>>  
>>  	/* Allocate memory for 2nd level table */
>>  	if (!table[idx]) {
>> -		page = alloc_pages_node(its->numa_node, GFP_KERNEL | __GFP_ZERO,
>> -					get_order(baser->psz));
>> +		page = its_alloc_pages_node(its->numa_node,
>> +					    GFP_KERNEL | __GFP_ZERO,
>> +					    get_order(baser->psz));
>>  		if (!page)
>>  			return false;
>>  
>> @@ -3418,7 +3450,9 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>>  	unsigned long *lpi_map = NULL;
>>  	unsigned long flags;
>>  	u16 *col_map = NULL;
>> +	struct page *page;
>>  	void *itt;
>> +	int itt_order;
>>  	int lpi_base;
>>  	int nr_lpis;
>>  	int nr_ites;
>> @@ -3430,7 +3464,6 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>>  	if (WARN_ON(!is_power_of_2(nvecs)))
>>  		nvecs = roundup_pow_of_two(nvecs);
>>  
>> -	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
>>  	/*
>>  	 * Even if the device wants a single LPI, the ITT must be
>>  	 * sized as a power of two (and you need at least one bit...).
>> @@ -3438,7 +3471,16 @@ 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_pages_node(its->numa_node,
>> +				    GFP_KERNEL | __GFP_ZERO,
>> +				    itt_order);
> 
> So we go from an allocation that was so far measured in *bytes* to
> something that is now at least a page. Per device. This seems a bit
> excessive to me, specially when it isn't conditioned on anything and
> is now imposed on all platforms, including the non-CCA systems (which
> are exactly 100% of the machines).

Catalin asked about this in v2:
https://lore.kernel.org/lkml/c329ae18-2b61-4851-8d6a-9e691a2007c8@xxxxxxx/

To be honest, I don't have a great handle on how much memory is being
wasted here. Within the realm guest I was testing this is rounding up an
otherwise 511 byte allocation to a 4k page, and there are 3 of them.
Which seems reasonable from a realm guest perspective.

I can see two options to improve here:

1. Add a !is_realm_world() check and return to the previous behaviour
when not running in a realm. It's ugly, and doesn't deal with any other
potential future memory encryption. cc_platform_has(CC_ATTR_MEM_ENCRYPT)
might be preferable? But this means no impact to non-realm guests.

2. Use a special (global) memory allocator that does the
set_memory_decrypted() dance on the pages that it allocates but allows
packing the allocations. I'm not aware of an existing kernel API for
this, so it's potentially quite a bit of code. The benefit is that it
reduces memory consumption in a realm guest, although fragmentation
still means we're likely to see a (small) growth.

Any thoughts on what you think would be best?

> Another thing is that if we go with page alignment, then the 256 byte
> alignment can obviously be removed everywhere (hint: MAPD needs to
> change).

Ah, good point - I'll need to look into that, my GIC-foo isn't quite up
to speed on that.

Thanks,

Steve