From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
catalin.marinas@arm.com, Sudeep Holla <sudeep.holla@arm.com>,
Robin Murphy <robin.murphy@arm.com>,
Jeremy Linton <jeremy.linton@arm.com>,
linux-acpi@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
linux-arm-kernel@lists.infradead.org,
Hanjun Guo <guohanjun@huawei.com>,
will@kernel.org, Christoph Hellwig <hch@lst.de>,
Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Subject: Re: [PATCH] arm64: mm: set ZONE_DMA size based on early IORT scan
Date: Tue, 13 Oct 2020 12:09:29 +0100 [thread overview]
Message-ID: <20201013110929.GB20319@e121166-lin.cambridge.arm.com> (raw)
In-Reply-To: <20201010093153.30177-1-ardb@kernel.org>
On Sat, Oct 10, 2020 at 11:31:53AM +0200, Ard Biesheuvel wrote:
> We recently introduced a 1 GB sized ZONE_DMA to cater for platforms
> incorporating masters that can address less than 32 bits of DMA, in
> particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has
> peripherals that can only address up to 1 GB (and its PCIe host
> bridge can only access the bottom 3 GB)
>
> Instructing the DMA layer about these limitations is straight-forward,
> even though we had to fix some issues regarding memory limits set in
> the IORT for named components, and regarding the handling of ACPI _DMA
> methods. However, the DMA layer also needs to be able to allocate
> memory that is guaranteed to meet those DMA constraints, for bounce
> buffering as well as allocating the backing for consistent mappings.
>
> This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately,
> it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes
> problems with kdump, and potentially in other places where allocations
> cannot cross zone boundaries. Therefore, we should avoid having two
> separate DMA zones when possible.
>
> So let's do an early scan of the IORT, and only create the ZONE_DMA
> if we encounter any devices that need it. This puts the burden on
> the firmware to describe such limitations in the IORT, which may be
> redundant (and less precise) if _DMA methods are also being provided.
> However, it should be noted that this situation is highly unusual for
> arm64 ACPI machines. Also, the DMA subsystem still gives precedence to
> the _DMA method if implemented, and so we will not lose the ability to
> perform streaming DMA outside the ZONE_DMA if the _DMA method permits
> it.
>
> Cc: Jeremy Linton <jeremy.linton@arm.com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Hanjun Guo <guohanjun@huawei.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> This is related to the discussion in
>
> https://lore.kernel.org/linux-arm-kernel/20201001161740.29064-2-nsaenzjulienne@suse.de/
>
> Documentation/arm64/arm-acpi.rst | 7 +++
> arch/arm64/mm/init.c | 8 +++
> drivers/acpi/arm64/iort.c | 51 ++++++++++++++++++++
> 3 files changed, 66 insertions(+)
Thanks for putting it together so promptly.
> diff --git a/Documentation/arm64/arm-acpi.rst b/Documentation/arm64/arm-acpi.rst
> index 47ecb9930dde..947f5b5c45ef 100644
> --- a/Documentation/arm64/arm-acpi.rst
> +++ b/Documentation/arm64/arm-acpi.rst
> @@ -205,6 +205,13 @@ devices available. This list of tables is not meant to be all inclusive;
> in some environments other tables may be needed (e.g., any of the APEI
> tables from section 18) to support specific functionality.
>
> +It is assumed that all DMA capable devices in the system are able to
> +access the lowest 4 GB of system memory. If this is not the case, an
> +IORT describing those limitations is mandatory, even if an IORT is not
> +otherwise necessary to describe the I/O topology, and regardless of
> +whether _DMA methods are used to describe the DMA limitations more
> +precisely. Once the system has booted, _DMA methods will take precedence
> +over DMA addressing limits described in the IORT.
If this is a boot requirement it must be in ARM's official documentation,
first, not the kernel one.
I understand this is an urgent (well - no comments on why bootstrapping
ACPI on Raspberry PI4 is causing all this fuss, honestly) fix but that's
not a reason to rush through these guidelines.
I would not add this paragraph to arm-acpi.rst, yet.
> ACPI Detection
> --------------
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index f0599ae73b8d..829fa63c3d72 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -191,6 +191,14 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
> unsigned long max_zone_pfns[MAX_NR_ZONES] = {0};
>
> #ifdef CONFIG_ZONE_DMA
> + if (IS_ENABLED(CONFIG_ACPI)) {
> + extern unsigned int acpi_iort_get_zone_dma_size(void);
Yes as Catalin asked please add a declaration in IORT headers.
> + zone_dma_bits = min(zone_dma_bits,
> + acpi_iort_get_zone_dma_size());
> + arm64_dma_phys_limit = max_zone_phys(zone_dma_bits);
> + }
> +
> max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
> #endif
> #ifdef CONFIG_ZONE_DMA32
> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index ec782e4a0fe4..c3db44896e49 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -1722,3 +1722,54 @@ void __init acpi_iort_init(void)
>
> iort_init_platform_devices();
> }
> +
> +#ifdef CONFIG_ZONE_DMA
> +/*
> + * Check the IORT whether any devices exist whose DMA mask is < 32 bits.
> + * If so, return the smallest value encountered, or 32 otherwise.
> + */
> +unsigned int __init acpi_iort_get_zone_dma_size(void)
> +{
> + struct acpi_table_iort *iort;
> + struct acpi_iort_node *node, *end;
> + acpi_status status;
> + u8 limit = 32;
> + int i;
> +
> + if (acpi_disabled)
> + return limit;
> +
> + status = acpi_get_table(ACPI_SIG_IORT, 0,
> + (struct acpi_table_header **)&iort);
> + if (ACPI_FAILURE(status))
> + return limit;
> +
> + node = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->node_offset);
> + end = ACPI_ADD_PTR(struct acpi_iort_node, iort, iort->header.length);
> +
> + for (i = 0; i < iort->node_count; i++) {
> + if (node >= end)
> + break;
> +
> + switch (node->type) {
> + struct acpi_iort_named_component *ncomp;
> + struct acpi_iort_root_complex *rc;
> +
> + case ACPI_IORT_NODE_NAMED_COMPONENT:
> + ncomp = (struct acpi_iort_named_component *)node->node_data;
> + if (ncomp->memory_address_limit)
> + limit = min(limit, ncomp->memory_address_limit);
> + break;
> +
> + case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
> + rc = (struct acpi_iort_root_complex *)node->node_data;
> + if (rc->memory_address_limit);
You need a node->revision check here otherwise we may end up
dereferencing junk. AKA ACPI versioning in all its glory.
Thanks,
Lorenzo
> + limit = min(limit, rc->memory_address_limit);
> + break;
> + }
> + node = ACPI_ADD_PTR(struct acpi_iort_node, node, node->length);
> + }
> + acpi_put_table(&iort->header);
> + return limit;
> +}
> +#endif
> --
> 2.17.1
>
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next prev parent reply other threads:[~2020-10-13 11:10 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-10 9:31 [PATCH] arm64: mm: set ZONE_DMA size based on early IORT scan Ard Biesheuvel
2020-10-12 9:28 ` Catalin Marinas
2020-10-12 9:30 ` Ard Biesheuvel
2020-10-12 10:43 ` Ard Biesheuvel
2020-10-12 11:24 ` Catalin Marinas
2020-10-12 14:19 ` Ard Biesheuvel
2020-10-12 15:49 ` Catalin Marinas
2020-10-12 15:55 ` Ard Biesheuvel
2020-10-12 16:22 ` Catalin Marinas
2020-10-12 16:35 ` Ard Biesheuvel
2020-10-12 16:59 ` Catalin Marinas
2020-10-13 14:42 ` Nicolas Saenz Julienne
2020-10-13 15:45 ` Catalin Marinas
2020-10-14 12:44 ` Ard Biesheuvel
2020-10-14 12:54 ` Nicolas Saenz Julienne
2020-10-12 12:16 ` kernel test robot
2020-10-13 11:09 ` Lorenzo Pieralisi [this message]
2020-10-13 11:22 ` Ard Biesheuvel
2020-10-13 11:38 ` Ard Biesheuvel
2020-10-13 11:43 ` Ard Biesheuvel
2020-10-13 13:13 ` Lorenzo Pieralisi
2020-10-13 13:42 ` Ard Biesheuvel
2020-10-13 15:11 ` Robin Murphy
2020-10-13 15:41 ` Lorenzo Pieralisi
2020-10-14 16:18 ` Catalin Marinas
2020-10-14 17:23 ` Lorenzo Pieralisi
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