From: Michael Kelley <mhklinux@outlook.com>
To: Will Deacon <will@kernel.org>,
Petr Tesarik <petrtesarik@huaweicloud.com>
Cc: Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Petr Tesarik <petr.tesarik1@huawei-partners.com>,
open list <linux-kernel@vger.kernel.org>,
"open list:DMA MAPPING HELPERS" <iommu@lists.linux.dev>,
Roberto Sassu <roberto.sassu@huaweicloud.com>,
Petr Tesarik <petr@tesarici.cz>
Subject: RE: [PATCH v3 0/2] swiotlb: allocate padding slots if necessary
Date: Fri, 22 Mar 2024 18:11:50 +0000 [thread overview]
Message-ID: <SN6PR02MB41574F4837E875F3D158B329D4312@SN6PR02MB4157.namprd02.prod.outlook.com> (raw)
In-Reply-To: <20240322150941.GA5634@willie-the-truck>
From: Will Deacon <will@kernel.org> Sent: Friday, March 22, 2024 8:10 AM
>
> Hi Petr,
>
> On Thu, Mar 21, 2024 at 06:19:00PM +0100, Petr Tesarik wrote:
> > From: Petr Tesarik <petr.tesarik1@huawei-partners.com>
> >
> > If the allocation alignment is bigger than IO_TLB_SIZE and min_align_mask
> > covers some bits in the original address between IO_TLB_SIZE and
> > alloc_align_mask, preserve these bits by allocating additional padding
> > slots before the actual swiotlb buffer.
>
> Thanks for fixing this! I was out at a conference last week, so I didn't
> get very far with it myself, but I ended up in a pickle trying to avoid
> extending 'struct io_tlb_slot'. Your solution is much better than the
> crazy avenue I started going down...
>
> With your changes, can we now simplify swiotlb_align_offset() to ignore
> dma_get_min_align_mask() altogether and just:
>
> return addr & (IO_TLB_SIZE - 1);
>
> ?
>
I don't think such a change is correct, since we want to allow the
DMA min_align_mask to work if it is set to 0x3FF or 0x1FF or
something else smaller than IO_TLB_SIZE - 1.
Petr's new offset calculation in swiotlb_tbl_map_single() is this:
offset = orig_addr & dma_get_min_align_mask(dev) &
(alloc_align_mask | (IO_TLB_SIZE - 1));
In the normal stream mapping case, where alloc_align_mask is
zero, Petr's new statement is equivalent to swiotlb_align_offset().
And I think it needs to continue to be equivalent so that
swiotlb_search_pool_area(), swiotlb_bounce() and
swiotlb_release_slots() calculate the same offset as
swiotlb_tbl_map_single() uses after it separately processes
the padding slots.
Perhaps a better approach to maintaining the equivalence is
to modify swiotlb_align_offset() to be Petr's new calculation,
with alloc_align_mask passed as an argument.
swiotlb_search_pool_area(), swiotlb_bounce(), and
swiotlb_release_slots() would all pass 0 as the alloc_align_mask
argument.
Michael
next prev parent reply other threads:[~2024-03-22 18:11 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-21 17:19 [PATCH v3 0/2] swiotlb: allocate padding slots if necessary Petr Tesarik
2024-03-21 17:19 ` [PATCH v3 1/2] swiotlb: extend buffer pre-padding to alloc_align_mask " Petr Tesarik
2024-03-22 4:29 ` Michael Kelley
2024-03-22 10:29 ` Petr Tesarik
2024-03-21 17:19 ` [PATCH v3 2/2] bug: introduce ASSERT_VAR_CAN_HOLD() Petr Tesarik
2024-03-22 4:33 ` Michael Kelley
2024-03-22 15:37 ` Will Deacon
2024-03-22 17:33 ` Petr Tesařík
2024-03-22 15:09 ` [PATCH v3 0/2] swiotlb: allocate padding slots if necessary Will Deacon
2024-03-22 17:51 ` Petr Tesařík
2024-03-27 19:42 ` Will Deacon
2024-03-22 18:11 ` Michael Kelley [this message]
2024-03-22 19:31 ` Petr Tesařík
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