Re: [PATCH v3] powerpc/pseries/iommu: Add TCEs for 16GB pages when RAM is pre-mapped

[Harsh Prateek Bora <harshpb@linux.ibm.com>]

+ Venkat

Hi Gaurav,
Would just like to confirm if it is tested with multiple iterations of 
hotplug of RAM (DLPAR) as well?

Hi Venkat,
Could you please help validate the patch for above-mentioned scenario as 
well?

Hi Shivaprasad,
Please share your review feedback or any additional testing scenarios 
needed?

Thanks
Harsh

On 15/05/26 9:21 pm, Gaurav Batra wrote:
> In powerPC, if Dynamic DMA Window is big enough, RAM is pre-mapped. To
> determine the size of RAM, a PAPR+ property "ibm,lrdr-capacity" is used.
> This OF property dictates what is the max size of RAM an LPAR can have,
> including DR added memory.
> 
> In PowerPC, 16GB pages can be allocated at machine level and then
> assigned to LPARs. These 16GB pages are added to LPAR memory at the time
> of boot. The address range for these 16GB pages is above MAX RAM an LPAR
> can have (ibm,lrdr-capacity). In the current implementation, these 16GB
> pages are being excluded from pre-mapped TCEs. A driver can have DMA
> buffers allocated from 16GB pages. This results in platform to raise an
> EEH when DMA is attempted on buffers in 16GB memory range.
> 
> commit 6aa989ab2bd0 ("powerpc/pseries/iommu: memory notifier incorrectly
> adds TCEs for pmemory")
> 
> Prior to the above patch, memblock_end_of_DRAM() was being used to
> determine the MAX memory of an LPAR. This included 16GB pages as well.
> The issue with using memblock_end_of_DRAM() is that when pmemory is
> converted to RAM via daxctl command, the DDW engine will incorrectly try
> to add TCEs for pmemory as well.
> 
> Below is the address distribution of RAM, 16GB pages and pmemory for an
> LPAR with max memory of 256GB, memory allocated 64GB, 2 16GB pages and
> assigned pmemory of 8GB.
> 
> RANGE                                 SIZE  STATE REMOVABLE     BLOCK
> 0x0000000000000000-0x0000000fffffffff  64G online       yes     0-255
> 0x0000004000000000-0x00000047ffffffff  32G online       yes 1024-1151
> 
> cat /sys/bus/nd/devices/region0/resource
> 0x40100000000
> cat /sys/bus/nd/devices/region0/size
> 8589934592
> 
> The approach to fix this problem is to revert back the code changes
> introduced by the above patch and to stash away the MAX memory of an
> LPAR, including 16GB pages, at the LPAR boot time. This value is then
> used whenever TCEs are needed to be pre-mapped - enable_DDW() or,
> iommu_mem_notifier()
> 
> Fixes: 6aa989ab2bd0 ("powerpc/pseries/iommu: memory notifier incorrectly adds TCEs for pmemory")
> Signed-off-by: Gaurav Batra <gbatra@linux.ibm.com>
> ---
> 
> Change log:
> 
> V2 -> V3
> 
> 1. Harsh: Remove R-b tags from the change log
> 
>     Response: Incorporated changes
> 
> 2. Harsh: Change WARN_ON() to WARN_ONCE()
> 
>     Response: Incorporated changes
> 
> 3. Harsh: Fix indendation
> 
>     Response: Incorporated changes
> 
> 4. Harsh: Replace comment with a log if limit < arg->nr_pages ?
> 
>     Response: Doesn't seems to be needed since the WARN_ONCE() will log this
>     scenario. I removed the comment instead.
> 
> V1 -> V2
> 
> 1. Harsh: Not only start_pfn, but end_pfn also needs to be within allowed
>     range, which may require clamping arg->nr_pages if crossing the limits.
> 
>     Response: Incorporated changes.
> 
>   arch/powerpc/platforms/pseries/iommu.c | 58 ++++++++++++++++++--------
>   1 file changed, 41 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> index 3e1f915fe4f6..7bbe070006fa 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -69,6 +69,8 @@ static struct iommu_table *iommu_pseries_alloc_table(int node)
>   	return tbl;
>   }
>   
> +static phys_addr_t pseries_ddw_max_ram;
> +
>   #ifdef CONFIG_IOMMU_API
>   static struct iommu_table_group_ops spapr_tce_table_group_ops;
>   #endif
> @@ -1285,13 +1287,17 @@ static LIST_HEAD(failed_ddw_pdn_list);
>   
>   static phys_addr_t ddw_memory_hotplug_max(void)
>   {
> -	resource_size_t max_addr;
> +	resource_size_t max_addr = memory_hotplug_max();
> +	struct device_node *memory;
>   
> -#if defined(CONFIG_NUMA) && defined(CONFIG_MEMORY_HOTPLUG)
> -	max_addr = hot_add_drconf_memory_max();
> -#else
> -	max_addr = memblock_end_of_DRAM();
> -#endif
> +	for_each_node_by_type(memory, "memory") {
> +		struct resource res;
> +
> +		if (of_address_to_resource(memory, 0, &res))
> +			continue;
> +
> +		max_addr = max_t(resource_size_t, max_addr, res.end + 1);
> +	}
>   
>   	return max_addr;
>   }
> @@ -1446,7 +1452,7 @@ static struct property *ddw_property_create(const char *propname, u32 liobn, u64
>   static bool enable_ddw(struct pci_dev *dev, struct device_node *pdn, u64 dma_mask)
>   {
>   	int len = 0, ret;
> -	int max_ram_len = order_base_2(ddw_memory_hotplug_max());
> +	int max_ram_len = order_base_2(pseries_ddw_max_ram);
>   	struct ddw_query_response query;
>   	struct ddw_create_response create;
>   	int page_shift;
> @@ -1668,7 +1674,7 @@ static bool enable_ddw(struct pci_dev *dev, struct device_node *pdn, u64 dma_mas
>   
>   	if (direct_mapping) {
>   		/* DDW maps the whole partition, so enable direct DMA mapping */
> -		ret = walk_system_ram_range(0, ddw_memory_hotplug_max() >> PAGE_SHIFT,
> +		ret = walk_system_ram_range(0, pseries_ddw_max_ram >> PAGE_SHIFT,
>   					    win64->value, tce_setrange_multi_pSeriesLP_walk);
>   		if (ret) {
>   			dev_info(&dev->dev, "failed to map DMA window for %pOF: %d\n",
> @@ -2419,23 +2425,35 @@ static int iommu_mem_notifier(struct notifier_block *nb, unsigned long action,
>   {
>   	struct dma_win *window;
>   	struct memory_notify *arg = data;
> +	unsigned long limit = arg->nr_pages;
> +	unsigned long max_ram_pages = pseries_ddw_max_ram >> PAGE_SHIFT;
>   	int ret = 0;
>   
>   	/* This notifier can get called when onlining persistent memory as well.
>   	 * TCEs are not pre-mapped for persistent memory. Persistent memory will
> -	 * always be above ddw_memory_hotplug_max()
> +	 * always be above pseries_ddw_max_ram
>   	 */
> +	if (arg->start_pfn >= max_ram_pages)
> +		return NOTIFY_OK;
> +
> +	/* RAM is being DLPAR'ed. The range should never exceed max ram.
> +	 * Just in case, clamp the range and throw a warning.
> +	 */
> +	if (arg->start_pfn + limit > max_ram_pages) {
> +		limit = max_ram_pages - arg->start_pfn;
> +		WARN_ONCE(1, "Limiting Page Range %lx - %lx to Max Mem Pages: %lx\n",
> +					arg->start_pfn, arg->start_pfn + arg->nr_pages,
> +					max_ram_pages);
> +	}
>   
>   	switch (action) {
>   	case MEM_GOING_ONLINE:
>   		spin_lock(&dma_win_list_lock);
>   		list_for_each_entry(window, &dma_win_list, list) {
> -			if (window->direct && (arg->start_pfn << PAGE_SHIFT) <
> -				ddw_memory_hotplug_max()) {
> +			if (window->direct) {
>   				ret |= tce_setrange_multi_pSeriesLP(arg->start_pfn,
> -						arg->nr_pages, window->prop);
> +						limit, window->prop);
>   			}
> -			/* XXX log error */
>   		}
>   		spin_unlock(&dma_win_list_lock);
>   		break;
> @@ -2443,12 +2461,10 @@ static int iommu_mem_notifier(struct notifier_block *nb, unsigned long action,
>   	case MEM_OFFLINE:
>   		spin_lock(&dma_win_list_lock);
>   		list_for_each_entry(window, &dma_win_list, list) {
> -			if (window->direct && (arg->start_pfn << PAGE_SHIFT) <
> -				ddw_memory_hotplug_max()) {
> +			if (window->direct) {
>   				ret |= tce_clearrange_multi_pSeriesLP(arg->start_pfn,
> -						arg->nr_pages, window->prop);
> +						limit, window->prop);
>   			}
> -			/* XXX log error */
>   		}
>   		spin_unlock(&dma_win_list_lock);
>   		break;
> @@ -2532,6 +2548,14 @@ void __init iommu_init_early_pSeries(void)
>   	register_memory_notifier(&iommu_mem_nb);
>   
>   	set_pci_dma_ops(&dma_iommu_ops);
> +
> +	/* During init determine the max memory an LPAR can have and set it. This
> +	 * will be used for pre-mapping RAM in DDW. memblock_end_of_DRAM() can
> +	 * change during the running of LPAR - daxctl can add pmemory as
> +	 * "system-ram". This memory range should not be pre-mapped in DDW since
> +	 * the address of pmemory can be much higher than the DDW size.
> +	 */
> +	pseries_ddw_max_ram = ddw_memory_hotplug_max();
>   }
>   
>   static int __init disable_multitce(char *str)
> 
> base-commit: 6d35786de28116ecf78797a62b84e6bf3c45aa5a