linux-kernel - Re: [PATCH v2 3/3] iommu: rockchip: Allocate tables from all available memory

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Message-ID: <f207165f-0c16-f81c-9828-1f99b278cabf@kwiboo.se>
Date:   Sat, 17 Jun 2023 15:30:10 +0000 (UTC)
From:   Jonas Karlman <jonas@...boo.se>
To:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>
Cc:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] iommu: rockchip: Allocate tables from all
 available memory

On 2023-06-16 12:58, Robin Murphy wrote:
> On 2023-06-15 23:26, Jonas Karlman wrote:
>> On 2023-06-15 23:25, Robin Murphy wrote:
>>> On 2023-06-15 21:10, Jonas Karlman wrote:
>>>> Newer Rockchip SoCs, RK356x and RK3588, support more then 4GB of memory.
>>>
>>> Older ones supposedly did too, e.g. commit 79db45be2b8b ("ARM: dts:
>>> rockchip: convert rk3288 device tree files to 64 bits"). Are we certain
>>> that nobody actually has a system with IOMMUv1 and more than 4GB of RAM?
>>
>> In IOMMU v1 bit 11:0 read back as 0 from MMU_DTE_ADDR reg, so I expect
>> that the old limit for v1 is 4GB.
> 
> Right, that was my point, sorry if it was unclear - on at least RK3288, 
> the *SoC* apparently supports RAM above 4GB, even if it's only the CPUs 
> that can access it. GFP_DMA32 technically *is* correct and appropriate 
> for IOMMUv1, so it's only safe to unconditionally remove it if we're 
> sure that, on all relevant IOMMUv1 SoCs in practice, no RAM above 4GB 
> exists such that ZONE_NORMAL is empty and all allocations come from 
> ZONE_DMA32 by default anyway.
> 
> (in truth this only matters for 64-bit SoCs, since on 32-bit there is no 
> ZONE_DMA32, but any >4GB RAM would already have to be in ZONE_HIGHMEM, 
> so safely out of scope)

Thanks for the insights!

I will keep the use of GFP_DMA32 flag on IOMMUv1 to be safe and only
remove it for IOMMUv2 in a v3 series.

Regards,
Jonas

> 
> Thanks,
> Robin.
> 
>> I will reword this to focus on IOMMU
>> v1 vs v2 instead of SoCs in v3.
>>
>>>
>>>> However, the RK IOMMU driver is using the GFP_DMA32 flag to limit
>>>> allocation of the discovery and page tables into memory below 4GB.
>>>>
>>>> Let's remove this limitation now that the discovery table address is
>>>
>>> Nit: s/discovery/directory/g again
>>
>> Will fix in v3 :-)
>>
>> Regards,
>> Jonas
>>
>>>
>>> Thanks,
>>> Robin.
>>>
>>>> correctly configured for addresses above 4GB.
>>>>
>>>> Signed-off-by: Jonas Karlman <jonas@...boo.se>
>>>> ---
>>>> v2:
>>>> - no change
>>>>
>>>>    drivers/iommu/rockchip-iommu.c | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
>>>> index 62be9bf42390..46498fc382ee 100644
>>>> --- a/drivers/iommu/rockchip-iommu.c
>>>> +++ b/drivers/iommu/rockchip-iommu.c
>>>> @@ -727,7 +727,7 @@ static u32 *rk_dte_get_page_table(struct rk_iommu_domain *rk_domain,
>>>>    	if (rk_dte_is_pt_valid(dte))
>>>>    		goto done;
>>>>    
>>>> -	page_table = (u32 *)get_zeroed_page(GFP_ATOMIC | GFP_DMA32);
>>>> +	page_table = (u32 *)get_zeroed_page(GFP_ATOMIC);
>>>>    	if (!page_table)
>>>>    		return ERR_PTR(-ENOMEM);
>>>>    
>>>> @@ -1076,7 +1076,7 @@ static struct iommu_domain *rk_iommu_domain_alloc(unsigned type)
>>>>    	 * Each level1 (dt) and level2 (pt) table has 1024 4-byte entries.
>>>>    	 * Allocate one 4 KiB page for each table.
>>>>    	 */
>>>> -	rk_domain->dt = (u32 *)get_zeroed_page(GFP_KERNEL | GFP_DMA32);
>>>> +	rk_domain->dt = (u32 *)get_zeroed_page(GFP_KERNEL);
>>>>    	if (!rk_domain->dt)
>>>>    		goto err_free_domain;
>>>>    
>>