Re: [PATCH v2 1/1] powerpc/iommu: Enable remaining IOMMU Pagesizes present in LoPAR

From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Michael Ellerman <mpe@ellerman.id.au>,
	Leonardo Bras <leobras.c@gmail.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	brking@linux.vnet.ibm.com
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/1] powerpc/iommu: Enable remaining IOMMU Pagesizes present in LoPAR
Date: Thu, 8 Apr 2021 17:13:40 +1000	[thread overview]
Message-ID: <8e1ce7e9-415b-92ea-0437-a4331ed3c7f9@ozlabs.ru> (raw)
In-Reply-To: <87im4xe3pk.fsf@mpe.ellerman.id.au>

On 08/04/2021 15:37, Michael Ellerman wrote:
> Leonardo Bras <leobras.c@gmail.com> writes:
>> According to LoPAR, ibm,query-pe-dma-window output named "IO Page Sizes"
>> will let the OS know all possible pagesizes that can be used for creating a
>> new DDW.
>>
>> Currently Linux will only try using 3 of the 8 available options:
>> 4K, 64K and 16M. According to LoPAR, Hypervisor may also offer 32M, 64M,
>> 128M, 256M and 16G.
> 
> Do we know of any hardware & hypervisor combination that will actually
> give us bigger pages?

On P8 16MB host pages and 16MB hardware iommu pages worked.

On P9, VM's 16MB IOMMU pages worked on top of 2MB host pages + 2MB 
hardware IOMMU pages.

> 
>> Enabling bigger pages would be interesting for direct mapping systems
>> with a lot of RAM, while using less TCE entries.
>>
>> Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
>> ---
>>   arch/powerpc/platforms/pseries/iommu.c | 49 ++++++++++++++++++++++----
>>   1 file changed, 42 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
>> index 9fc5217f0c8e..6cda1c92597d 100644
>> --- a/arch/powerpc/platforms/pseries/iommu.c
>> +++ b/arch/powerpc/platforms/pseries/iommu.c
>> @@ -53,6 +53,20 @@ enum {
>>   	DDW_EXT_QUERY_OUT_SIZE = 2
>>   };
> 
> A comment saying where the values come from would be good.
> 
>> +#define QUERY_DDW_PGSIZE_4K	0x01
>> +#define QUERY_DDW_PGSIZE_64K	0x02
>> +#define QUERY_DDW_PGSIZE_16M	0x04
>> +#define QUERY_DDW_PGSIZE_32M	0x08
>> +#define QUERY_DDW_PGSIZE_64M	0x10
>> +#define QUERY_DDW_PGSIZE_128M	0x20
>> +#define QUERY_DDW_PGSIZE_256M	0x40
>> +#define QUERY_DDW_PGSIZE_16G	0x80
> 
> I'm not sure the #defines really gain us much vs just putting the
> literal values in the array below?

Then someone says "uuuuu magic values" :) I do not mind either way. Thanks,

>> +struct iommu_ddw_pagesize {
>> +	u32 mask;
>> +	int shift;
>> +};
>> +
>>   static struct iommu_table_group *iommu_pseries_alloc_group(int node)
>>   {
>>   	struct iommu_table_group *table_group;
>> @@ -1099,6 +1113,31 @@ static void reset_dma_window(struct pci_dev *dev, struct device_node *par_dn)
>>   			 ret);
>>   }
>>   
>> +/* Returns page shift based on "IO Page Sizes" output at ibm,query-pe-dma-window. See LoPAR */
>> +static int iommu_get_page_shift(u32 query_page_size)
>> +{
>> +	const struct iommu_ddw_pagesize ddw_pagesize[] = {
>> +		{ QUERY_DDW_PGSIZE_16G,  __builtin_ctz(SZ_16G)  },
>> +		{ QUERY_DDW_PGSIZE_256M, __builtin_ctz(SZ_256M) },
>> +		{ QUERY_DDW_PGSIZE_128M, __builtin_ctz(SZ_128M) },
>> +		{ QUERY_DDW_PGSIZE_64M,  __builtin_ctz(SZ_64M)  },
>> +		{ QUERY_DDW_PGSIZE_32M,  __builtin_ctz(SZ_32M)  },
>> +		{ QUERY_DDW_PGSIZE_16M,  __builtin_ctz(SZ_16M)  },
>> +		{ QUERY_DDW_PGSIZE_64K,  __builtin_ctz(SZ_64K)  },
>> +		{ QUERY_DDW_PGSIZE_4K,   __builtin_ctz(SZ_4K)   }
>> +	};
> 
> 
> cheers
> 

-- 
Alexey