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Date:   Thu, 23 Sep 2021 10:52:47 -0500
From:   "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>
To:     Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org,
        Felix.Kuehling@....com, linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jgg@...dia.com, jglisse@...hat.com
Subject: Re: [PATCH v2 09/12] lib: test_hmm add module param for zone device
 type


On 9/21/2021 12:14 AM, Alistair Popple wrote:
> On Tuesday, 21 September 2021 6:05:30 AM AEST Sierra Guiza, Alejandro (Alex) wrote:
>> On 9/20/2021 3:53 AM, Alistair Popple wrote:
>>> On Tuesday, 14 September 2021 2:16:01 AM AEST Alex Sierra wrote:
>>>> In order to configure device public in test_hmm, two module parameters
>>>> should be passed, which correspond to the SP start address of each
>>>> device (2) spm_addr_dev0 & spm_addr_dev1. If no parameters are passed,
>>>> private device type is configured.
>>> It's a pity that testing this seems to require some amount of special setup to
>>> test. Is there a way this could be made to work on a more standard setup
>>> similar to how DEVICE_PRIVATE is tested?
>> Hi Alistair
>> We tried to do it as simpler as possible. Unfortunately, there are two main
>> requirements to register dev memory as DEVICE_PUBLIC type. This memory must
>> NOT be accessed by any memory allocator (SLAB, SLOB, SLUB) plus, it has
>> to be
>> CPU coherently accessed.  We also want to avoid aliasing the same PFNs for
>> different page types (regular system memory and DEVICE_PUBLIC). So we don't
>> want the reserved memory to be part of the kernel's memory map before we
>> call
>> memremap_pages. A transparent way of doing it, without any special HW, was
>> setting a portion of system memory as SPM (Special purpose memory). And use
>> this as our “device fake” memory.
> Ok, I think it's great that we can test this without special HW but the boot
> time configuration is still a bit annoying. Would it be possible to allocate
> memory fitting the above requirements by hot unplugging it with something like
> offline_and_remove_memory()?
>
> I also don't see why the DEVICE_PRIVATE and DEVICE_PUBLIC testing should be
> mutually exclusive - why can't we test both without reloading the module?
You could do both DEVICE_PRIVATE and DEVICE_PUBLIC tests by running the 
test_hmm_sh
script twice, just passing the proper parameters. Even when you booted 
with fake EFI SP
regions. If spm_address_dev0/1 parameters are passed, the module gets 
configured with
DEVICE_PUBLIC type. Otherwise DEVICE_PRIVATE type is set. Technically 
the only
complication in testing DEVICE_PUBLIC is the fake SPM boot parameter.

Alex Sierra
>
>   - Alistair
>
>> Regards,
>> Alex Sierra
>>
>>>> Signed-off-by: Alex Sierra <alex.sierra@....com>
>>>> ---
>>>> v5:
>>>> Remove devmem->pagemap.type = MEMORY_DEVICE_PRIVATE at
>>>> dmirror_allocate_chunk that was forcing to configure pagemap.type
>>>> to MEMORY_DEVICE_PRIVATE
>>>>
>>>> v6:
>>>> Check for null pointers for resource and memremap references
>>>> at dmirror_allocate_chunk
>>>>
>>>> v7:
>>>> Due to patch dropped from these patch series "kernel: resource:
>>>> lookup_resource as exported symbol", lookup_resource was not longer a
>>>> callable function. This was used in public device configuration, to
>>>> get start and end addresses, to create pgmap->range struct. This
>>>> information is now taken directly from the spm_addr_devX parameters and
>>>> the fixed size DEVMEM_CHUNK_SIZE.
>>>> ---
>>>>    lib/test_hmm.c      | 66 +++++++++++++++++++++++++++++++--------------
>>>>    lib/test_hmm_uapi.h |  1 +
>>>>    2 files changed, 47 insertions(+), 20 deletions(-)
>>>>
>>>> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
>>>> index 3cd91ca31dd7..ef27e355738a 100644
>>>> --- a/lib/test_hmm.c
>>>> +++ b/lib/test_hmm.c
>>>> @@ -33,6 +33,16 @@
>>>>    #define DEVMEM_CHUNK_SIZE		(256 * 1024 * 1024U)
>>>>    #define DEVMEM_CHUNKS_RESERVE		16
>>>>    
>>>> +static unsigned long spm_addr_dev0;
>>>> +module_param(spm_addr_dev0, long, 0644);
>>>> +MODULE_PARM_DESC(spm_addr_dev0,
>>>> +		"Specify start address for SPM (special purpose memory) used for device 0. By setting this Generic device type will be used. Make sure spm_addr_dev1 is set too");
>>>> +
>>>> +static unsigned long spm_addr_dev1;
>>>> +module_param(spm_addr_dev1, long, 0644);
>>>> +MODULE_PARM_DESC(spm_addr_dev1,
>>>> +		"Specify start address for SPM (special purpose memory) used for device 1. By setting this Generic device type will be used. Make sure spm_addr_dev0 is set too");
>>>> +
>>>>    static const struct dev_pagemap_ops dmirror_devmem_ops;
>>>>    static const struct mmu_interval_notifier_ops dmirror_min_ops;
>>>>    static dev_t dmirror_dev;
>>>> @@ -450,11 +460,11 @@ static int dmirror_write(struct dmirror *dmirror, struct hmm_dmirror_cmd *cmd)
>>>>    	return ret;
>>>>    }
>>>>    
>>>> -static bool dmirror_allocate_chunk(struct dmirror_device *mdevice,
>>>> +static int dmirror_allocate_chunk(struct dmirror_device *mdevice,
>>>>    				   struct page **ppage)
>>>>    {
>>>>    	struct dmirror_chunk *devmem;
>>>> -	struct resource *res;
>>>> +	struct resource *res = NULL;
>>>>    	unsigned long pfn;
>>>>    	unsigned long pfn_first;
>>>>    	unsigned long pfn_last;
>>>> @@ -462,17 +472,29 @@ static bool dmirror_allocate_chunk(struct dmirror_device *mdevice,
>>>>    
>>>>    	devmem = kzalloc(sizeof(*devmem), GFP_KERNEL);
>>>>    	if (!devmem)
>>>> -		return false;
>>>> +		return -ENOMEM;
>>>>    
>>>> -	res = request_free_mem_region(&iomem_resource, DEVMEM_CHUNK_SIZE,
>>>> -				      "hmm_dmirror");
>>>> -	if (IS_ERR(res))
>>>> -		goto err_devmem;
>>>> +	if (!spm_addr_dev0 && !spm_addr_dev1) {
>>>> +		res = request_free_mem_region(&iomem_resource, DEVMEM_CHUNK_SIZE,
>>>> +					      "hmm_dmirror");
>>>> +		if (IS_ERR_OR_NULL(res))
>>>> +			goto err_devmem;
>>>> +		devmem->pagemap.range.start = res->start;
>>>> +		devmem->pagemap.range.end = res->end;
>>>> +		devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
>>>> +		mdevice->zone_device_type = HMM_DMIRROR_MEMORY_DEVICE_PRIVATE;
>>>> +	} else if (spm_addr_dev0 && spm_addr_dev1) {
>>>> +		devmem->pagemap.range.start = MINOR(mdevice->cdevice.dev) ?
>>>> +							spm_addr_dev0 :
>>>> +							spm_addr_dev1;
>>>> +		devmem->pagemap.range.end = devmem->pagemap.range.start +
>>>> +					    DEVMEM_CHUNK_SIZE - 1;
>>>> +		devmem->pagemap.type = MEMORY_DEVICE_PUBLIC;
>>>> +		mdevice->zone_device_type = HMM_DMIRROR_MEMORY_DEVICE_PUBLIC;
>>>> +	} else {
>>>> +		pr_err("Both spm_addr_dev parameters should be set\n");
>>>> +	}
>>>>    
>>>> -	mdevice->zone_device_type = HMM_DMIRROR_MEMORY_DEVICE_PRIVATE;
>>>> -	devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
>>>> -	devmem->pagemap.range.start = res->start;
>>>> -	devmem->pagemap.range.end = res->end;
>>>>    	devmem->pagemap.nr_range = 1;
>>>>    	devmem->pagemap.ops = &dmirror_devmem_ops;
>>>>    	devmem->pagemap.owner = mdevice;
>>>> @@ -493,10 +515,14 @@ static bool dmirror_allocate_chunk(struct dmirror_device *mdevice,
>>>>    		mdevice->devmem_capacity = new_capacity;
>>>>    		mdevice->devmem_chunks = new_chunks;
>>>>    	}
>>>> -
>>>>    	ptr = memremap_pages(&devmem->pagemap, numa_node_id());
>>>> -	if (IS_ERR(ptr))
>>>> +	if (IS_ERR_OR_NULL(ptr)) {
>>>> +		if (ptr)
>>>> +			ret = PTR_ERR(ptr);
>>>> +		else
>>>> +			ret = -EFAULT;
>>>>    		goto err_release;
>>>> +	}
>>>>    
>>>>    	devmem->mdevice = mdevice;
>>>>    	pfn_first = devmem->pagemap.range.start >> PAGE_SHIFT;
>>>> @@ -529,7 +555,8 @@ static bool dmirror_allocate_chunk(struct dmirror_device *mdevice,
>>>>    
>>>>    err_release:
>>>>    	mutex_unlock(&mdevice->devmem_lock);
>>>> -	release_mem_region(devmem->pagemap.range.start, range_len(&devmem->pagemap.range));
>>>> +	if (res)
>>>> +		release_mem_region(devmem->pagemap.range.start, range_len(&devmem->pagemap.range));
>>>>    err_devmem:
>>>>    	kfree(devmem);
>>>>    
>>>> @@ -1097,10 +1124,8 @@ static int dmirror_device_init(struct dmirror_device *mdevice, int id)
>>>>    	if (ret)
>>>>    		return ret;
>>>>    
>>>> -	/* Build a list of free ZONE_DEVICE private struct pages */
>>>> -	dmirror_allocate_chunk(mdevice, NULL);
>>>> -
>>>> -	return 0;
>>>> +	/* Build a list of free ZONE_DEVICE struct pages */
>>>> +	return dmirror_allocate_chunk(mdevice, NULL);
>>>>    }
>>>>    
>>>>    static void dmirror_device_remove(struct dmirror_device *mdevice)
>>>> @@ -1113,8 +1138,9 @@ static void dmirror_device_remove(struct dmirror_device *mdevice)
>>>>    				mdevice->devmem_chunks[i];
>>>>    
>>>>    			memunmap_pages(&devmem->pagemap);
>>>> -			release_mem_region(devmem->pagemap.range.start,
>>>> -					   range_len(&devmem->pagemap.range));
>>>> +			if (devmem->pagemap.type == MEMORY_DEVICE_PRIVATE)
>>>> +				release_mem_region(devmem->pagemap.range.start,
>>>> +						   range_len(&devmem->pagemap.range));
>>>>    			kfree(devmem);
>>>>    		}
>>>>    		kfree(mdevice->devmem_chunks);
>>>> diff --git a/lib/test_hmm_uapi.h b/lib/test_hmm_uapi.h
>>>> index ee88701793d5..00259d994410 100644
>>>> --- a/lib/test_hmm_uapi.h
>>>> +++ b/lib/test_hmm_uapi.h
>>>> @@ -65,6 +65,7 @@ enum {
>>>>    enum {
>>>>    	/* 0 is reserved to catch uninitialized type fields */
>>>>    	HMM_DMIRROR_MEMORY_DEVICE_PRIVATE = 1,
>>>> +	HMM_DMIRROR_MEMORY_DEVICE_PUBLIC,
>>>>    };
>>>>    
>>>>    #endif /* _LIB_TEST_HMM_UAPI_H */
>>>>
>>>
>>>
>
>
>

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