include/linux/swiotlb.h | 2 +- kernel/dma/Kconfig | 7 +++++++ 2 files changed, 8 insertions(+), 1 deletion(-)
From: Li Hua Qian <huaqian.li@siemens.com> This patchset introduces a change to make the IO_TLB_SEGSIZE parameter configurable via a new kernel configuration option (CONFIG_SWIOTLB_SEGSIZE). In certain applications, the default value of IO_TLB_SEGSIZE (128) may not be sufficient for memory allocation, leading to runtime errors. By making this parameter configurable, users can adjust the segment size to better suit their specific use cases, improving flexibility and system stability. Li Hua Qian (1): swiotlb: Make IO_TLB_SEGSIZE configurable include/linux/swiotlb.h | 2 +- kernel/dma/Kconfig | 7 +++++++ 2 files changed, 8 insertions(+), 1 deletion(-) -- 2.34.1
On 22.04.2025 08:37, huaqian.li@siemens.com wrote: > From: Li Hua Qian <huaqian.li@siemens.com> > > This patchset introduces a change to make the IO_TLB_SEGSIZE parameter > configurable via a new kernel configuration option (CONFIG_SWIOTLB_SEGSIZE). > > In certain applications, the default value of IO_TLB_SEGSIZE (128) may > not be sufficient for memory allocation, leading to runtime errors. By > making this parameter configurable, users can adjust the segment size to > better suit their specific use cases, improving flexibility and system > stability. Could You elaborate a bit more what are those certain applications that require increasing IO_TLB_SEGSIZE? I'm not against it, but such change should be well justified and described, while the above cover-letter doesn't provide anything more than is written in the patch description. > Li Hua Qian (1): > swiotlb: Make IO_TLB_SEGSIZE configurable > > include/linux/swiotlb.h | 2 +- > kernel/dma/Kconfig | 7 +++++++ > 2 files changed, 8 insertions(+), 1 deletion(-) > Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
On Tue, 2025-04-22 at 15:36 +0200, Marek Szyprowski wrote: > On 22.04.2025 08:37, huaqian.li@siemens.com wrote: > > From: Li Hua Qian <huaqian.li@siemens.com> > > > > This patchset introduces a change to make the IO_TLB_SEGSIZE > > parameter > > configurable via a new kernel configuration option > > (CONFIG_SWIOTLB_SEGSIZE). > > > > In certain applications, the default value of IO_TLB_SEGSIZE (128) > > may > > not be sufficient for memory allocation, leading to runtime errors. > > By > > making this parameter configurable, users can adjust the segment > > size to > > better suit their specific use cases, improving flexibility and > > system > > stability. > > Could You elaborate a bit more what are those certain applications > that > require increasing IO_TLB_SEGSIZE? I'm not against it, but such > change > should be well justified and described, while the above cover-letter > doesn't provide anything more than is written in the patch > description. Thank you for your feedback, Marek. To provide more context, one specific application that requires increasing IO_TLB_SEGSIZE is the Hailo 8 PCIe AI card. This card uses dma_alloc_coherent to allocate descriptor lists, as seen in the Hailo driver implementation here: https://github.com/hailo-ai/hailort-drivers/blob/7161f9ee5918029bd4497f590003c2f87ec32507/linux/vdma/memory.c#L322 The maximum size (nslots) for these allocations can reach 160, which exceeds the current default value of IO_TLB_SEGSIZE (128). Since IO_TLB_SEGSIZE is defined as a constant in the kernel: `#define IO_TLB_SEGSIZE 128` this limitation causes swiotlb_search_pool_area, https://github.com/torvalds/linux/blame/v6.15-rc2/kernel/dma/swiotlb.c#L1085, (or swiotlb_do_find_slots in older kernels) to fail when attempting to allocate contiguous physical memory (CMA). This results in runtime errors and prevents the Hailo 8 card from functioning correctly in certain configurations. By making IO_TLB_SEGSIZE configurable via a kernel configuration option (CONFIG_SWIOTLB_SEGSIZE), users can adjust the segment size to accommodate such use cases. This change improves flexibility and ensures that systems can be tailored to meet the requirements of specific hardware, such as the Hailo 8 PCIe AI card, without requiring kernel source modifications. I hope this example clarifies the need for this change. Please let me know if further details or additional examples are required. Best Regards, Li Hua Qian > > > > Li Hua Qian (1): > > swiotlb: Make IO_TLB_SEGSIZE configurable > > > > include/linux/swiotlb.h | 2 +- > > kernel/dma/Kconfig | 7 +++++++ > > 2 files changed, 8 insertions(+), 1 deletion(-) > > > Best regards -- Hua Qian Li Siemens AG www.siemens.com
On 24/04/2025 6:12 am, Li, Hua Qian wrote: > On Tue, 2025-04-22 at 15:36 +0200, Marek Szyprowski wrote: >> On 22.04.2025 08:37, huaqian.li@siemens.com wrote: >>> From: Li Hua Qian <huaqian.li@siemens.com> >>> >>> This patchset introduces a change to make the IO_TLB_SEGSIZE >>> parameter >>> configurable via a new kernel configuration option >>> (CONFIG_SWIOTLB_SEGSIZE). >>> >>> In certain applications, the default value of IO_TLB_SEGSIZE (128) >>> may >>> not be sufficient for memory allocation, leading to runtime errors. >>> By >>> making this parameter configurable, users can adjust the segment >>> size to >>> better suit their specific use cases, improving flexibility and >>> system >>> stability. >> >> Could You elaborate a bit more what are those certain applications >> that >> require increasing IO_TLB_SEGSIZE? I'm not against it, but such >> change >> should be well justified and described, while the above cover-letter >> doesn't provide anything more than is written in the patch >> description. > Thank you for your feedback, Marek. > > To provide more context, one specific application that requires > increasing IO_TLB_SEGSIZE is the Hailo 8 PCIe AI card. This card uses > dma_alloc_coherent to allocate descriptor lists, as seen in the Hailo > driver implementation here: > https://github.com/hailo-ai/hailort-drivers/blob/7161f9ee5918029bd4497f590003c2f87ec32507/linux/vdma/memory.c#L322 > The maximum size (nslots) for these allocations can reach 160, which > exceeds the current default value of IO_TLB_SEGSIZE (128). > > Since IO_TLB_SEGSIZE is defined as a constant in the kernel: > > `#define IO_TLB_SEGSIZE 128` > > > this limitation causes swiotlb_search_pool_area, > https://github.com/torvalds/linux/blame/v6.15-rc2/kernel/dma/swiotlb.c#L1085, > (or swiotlb_do_find_slots in older kernels) to fail when attempting to > allocate contiguous physical memory (CMA). This results in runtime > errors and prevents the Hailo 8 card from functioning correctly in > certain configurations. Hmm, dma_alloc_coherent() should really not be trying to allocate from SWIOTLB in the first place - how is that happening? If you're using restricted DMA for a device which wants significant coherent allocations, then it wants to have it's own shared-dma-pool for those *as well* as the restricted-dma-pool for bouncing streaming DMA. Thanks, Robin. > By making IO_TLB_SEGSIZE configurable via a kernel configuration option > (CONFIG_SWIOTLB_SEGSIZE), users can adjust the segment size to > accommodate such use cases. This change improves flexibility and > ensures that systems can be tailored to meet the requirements of > specific hardware, such as the Hailo 8 PCIe AI card, without requiring > kernel source modifications. > > I hope this example clarifies the need for this change. Please let me > know if further details or additional examples are required. > > Best Regards, > Li Hua Qian >> >> >>> Li Hua Qian (1): >>> swiotlb: Make IO_TLB_SEGSIZE configurable >>> >>> include/linux/swiotlb.h | 2 +- >>> kernel/dma/Kconfig | 7 +++++++ >>> 2 files changed, 8 insertions(+), 1 deletion(-) >>> >> Best regards >
On Thu, 2025-04-24 at 13:58 +0100, Robin Murphy wrote: > On 24/04/2025 6:12 am, Li, Hua Qian wrote: > > On Tue, 2025-04-22 at 15:36 +0200, Marek Szyprowski wrote: > > > On 22.04.2025 08:37, huaqian.li@siemens.com wrote: > > > > From: Li Hua Qian <huaqian.li@siemens.com> > > > > > > > > This patchset introduces a change to make the IO_TLB_SEGSIZE > > > > parameter > > > > configurable via a new kernel configuration option > > > > (CONFIG_SWIOTLB_SEGSIZE). > > > > > > > > In certain applications, the default value of IO_TLB_SEGSIZE > > > > (128) > > > > may > > > > not be sufficient for memory allocation, leading to runtime > > > > errors. > > > > By > > > > making this parameter configurable, users can adjust the > > > > segment > > > > size to > > > > better suit their specific use cases, improving flexibility and > > > > system > > > > stability. > > > > > > Could You elaborate a bit more what are those certain > > > applications > > > that > > > require increasing IO_TLB_SEGSIZE? I'm not against it, but such > > > change > > > should be well justified and described, while the above cover- > > > letter > > > doesn't provide anything more than is written in the patch > > > description. > > Thank you for your feedback, Marek. > > > > To provide more context, one specific application that requires > > increasing IO_TLB_SEGSIZE is the Hailo 8 PCIe AI card. This card > > uses > > dma_alloc_coherent to allocate descriptor lists, as seen in the > > Hailo > > driver implementation here: > > https://github.com/hailo-ai/hailort-drivers/blob/7161f9ee5918029bd4497f590003c2f87ec32507/linux/vdma/memory.c#L322 > > The maximum size (nslots) for these allocations can reach 160, > > which > > exceeds the current default value of IO_TLB_SEGSIZE (128). > > > > Since IO_TLB_SEGSIZE is defined as a constant in the kernel: > > > > `#define IO_TLB_SEGSIZE 128` > > > > > > this limitation causes swiotlb_search_pool_area, > > https://github.com/torvalds/linux/blame/v6.15-rc2/kernel/dma/swiotlb.c#L1085 > > , > > (or swiotlb_do_find_slots in older kernels) to fail when attempting > > to > > allocate contiguous physical memory (CMA). This results in runtime > > errors and prevents the Hailo 8 card from functioning correctly in > > certain configurations. > > Hmm, dma_alloc_coherent() should really not be trying to allocate > from > SWIOTLB in the first place - how is that happening? > > If you're using restricted DMA for a device which wants significant > coherent allocations, then it wants to have it's own shared-dma-pool > for > those *as well* as the restricted-dma-pool for bouncing streaming > DMA. > > Thanks, > Robin. Hi Robin, Regarding the specific Hailo Card case, the issue arises due to the capabilities of certain SoCs or CPUs. For example, many K3 SoCs lack an IOMMU, which is typically used to isolate the system against DMA-based attacks of external PCI devices. Taking the TI AM65 as an example, it doesn't have an IOMMU, but instead includes a Peripheral Virtualization Unit (PVU). The PVU provides functionality similar to an IOMMU and is used to isolate PCI devices from the Linux host, and the SWIOTLB is used to manp all DMA buffers from a static memory carve-out. You can find more details and background information here: https://lore.kernel.org/all/20250422061406.112539-1-huaqian.li@siemens.com/ > > > By making IO_TLB_SEGSIZE configurable via a kernel configuration > > option > > (CONFIG_SWIOTLB_SEGSIZE), users can adjust the segment size to > > accommodate such use cases. This change improves flexibility and > > ensures that systems can be tailored to meet the requirements of > > specific hardware, such as the Hailo 8 PCIe AI card, without > > requiring > > kernel source modifications. > > > > I hope this example clarifies the need for this change. Please let > > me > > know if further details or additional examples are required. > > > > Best Regards, > > Li Hua Qian > > > > > > > > > > Li Hua Qian (1): > > > > swiotlb: Make IO_TLB_SEGSIZE configurable > > > > > > > > include/linux/swiotlb.h | 2 +- > > > > kernel/dma/Kconfig | 7 +++++++ > > > > 2 files changed, 8 insertions(+), 1 deletion(-) > > > > > > > Best regards > > -- Hua Qian Li Siemens AG http://www.siemens.com/
On 2025-04-25 6:32 am, Li, Hua Qian wrote: > On Thu, 2025-04-24 at 13:58 +0100, Robin Murphy wrote: >> On 24/04/2025 6:12 am, Li, Hua Qian wrote: >>> On Tue, 2025-04-22 at 15:36 +0200, Marek Szyprowski wrote: >>>> On 22.04.2025 08:37, huaqian.li@siemens.com wrote: >>>>> From: Li Hua Qian <huaqian.li@siemens.com> >>>>> >>>>> This patchset introduces a change to make the IO_TLB_SEGSIZE >>>>> parameter >>>>> configurable via a new kernel configuration option >>>>> (CONFIG_SWIOTLB_SEGSIZE). >>>>> >>>>> In certain applications, the default value of IO_TLB_SEGSIZE >>>>> (128) >>>>> may >>>>> not be sufficient for memory allocation, leading to runtime >>>>> errors. >>>>> By >>>>> making this parameter configurable, users can adjust the >>>>> segment >>>>> size to >>>>> better suit their specific use cases, improving flexibility and >>>>> system >>>>> stability. >>>> >>>> Could You elaborate a bit more what are those certain >>>> applications >>>> that >>>> require increasing IO_TLB_SEGSIZE? I'm not against it, but such >>>> change >>>> should be well justified and described, while the above cover- >>>> letter >>>> doesn't provide anything more than is written in the patch >>>> description. >>> Thank you for your feedback, Marek. >>> >>> To provide more context, one specific application that requires >>> increasing IO_TLB_SEGSIZE is the Hailo 8 PCIe AI card. This card >>> uses >>> dma_alloc_coherent to allocate descriptor lists, as seen in the >>> Hailo >>> driver implementation here: >>> https://github.com/hailo-ai/hailort-drivers/blob/7161f9ee5918029bd4497f590003c2f87ec32507/linux/vdma/memory.c#L322 >>> The maximum size (nslots) for these allocations can reach 160, >>> which >>> exceeds the current default value of IO_TLB_SEGSIZE (128). >>> >>> Since IO_TLB_SEGSIZE is defined as a constant in the kernel: >>> >>> `#define IO_TLB_SEGSIZE 128` >>> >>> >>> this limitation causes swiotlb_search_pool_area, >>> https://github.com/torvalds/linux/blame/v6.15-rc2/kernel/dma/swiotlb.c#L1085 >>> , >>> (or swiotlb_do_find_slots in older kernels) to fail when attempting >>> to >>> allocate contiguous physical memory (CMA). This results in runtime >>> errors and prevents the Hailo 8 card from functioning correctly in >>> certain configurations. >> >> Hmm, dma_alloc_coherent() should really not be trying to allocate >> from >> SWIOTLB in the first place - how is that happening? >> >> If you're using restricted DMA for a device which wants significant >> coherent allocations, then it wants to have it's own shared-dma-pool >> for >> those *as well* as the restricted-dma-pool for bouncing streaming >> DMA. >> >> Thanks, >> Robin. > > Hi Robin, > > Regarding the specific Hailo Card case, the issue arises due > to the capabilities of certain SoCs or CPUs. For example, many > K3 SoCs lack an IOMMU, which is typically used to isolate the > system against DMA-based attacks of external PCI devices. > > Taking the TI AM65 as an example, it doesn't have an IOMMU, but > instead includes a Peripheral Virtualization Unit (PVU). The > PVU provides functionality similar to an IOMMU and is used to > isolate PCI devices from the Linux host, and the SWIOTLB is > used to manp all DMA buffers from a static memory carve-out. And as I said, if you want to support general coherent allocations then you should use part of that carveout for a regular coherent DMA pool. The restricted pool is only intended for streaming DMA - swiotlb_alloc() is only meant as a convenience fallback for the kind of devices which mostly do streaming DMA but make one or two small coherent allocations from a suitable context. It does not work for *all* valid usage of dma_alloc_attrs(), and if you want to do this for arbitrary PCI devices then you almost certainly *do* need to be able to support drivers which make allocations in atomic context. Thanks, Robin. > You can find more details and background information here: > https://lore.kernel.org/all/20250422061406.112539-1-huaqian.li@siemens.com/ > >> >>> By making IO_TLB_SEGSIZE configurable via a kernel configuration >>> option >>> (CONFIG_SWIOTLB_SEGSIZE), users can adjust the segment size to >>> accommodate such use cases. This change improves flexibility and >>> ensures that systems can be tailored to meet the requirements of >>> specific hardware, such as the Hailo 8 PCIe AI card, without >>> requiring >>> kernel source modifications. >>> >>> I hope this example clarifies the need for this change. Please let >>> me >>> know if further details or additional examples are required. >>> >>> Best Regards, >>> Li Hua Qian >>>> >>>> >>>>> Li Hua Qian (1): >>>>> swiotlb: Make IO_TLB_SEGSIZE configurable >>>>> >>>>> include/linux/swiotlb.h | 2 +- >>>>> kernel/dma/Kconfig | 7 +++++++ >>>>> 2 files changed, 8 insertions(+), 1 deletion(-) >>>>> >>>> Best regards >>> > > -- > Hua Qian Li > Siemens AG > http://www.siemens.com/
On Fri, Apr 25, 2025 at 11:42:24AM +0100, Robin Murphy wrote: > On 2025-04-25 6:32 am, Li, Hua Qian wrote: > > On Thu, 2025-04-24 at 13:58 +0100, Robin Murphy wrote: > > > On 24/04/2025 6:12 am, Li, Hua Qian wrote: > > > > On Tue, 2025-04-22 at 15:36 +0200, Marek Szyprowski wrote: > > > > > On 22.04.2025 08:37, huaqian.li@siemens.com wrote: > > > > > > From: Li Hua Qian <huaqian.li@siemens.com> > > > > > > > > > > > > This patchset introduces a change to make the IO_TLB_SEGSIZE > > > > > > parameter > > > > > > configurable via a new kernel configuration option > > > > > > (CONFIG_SWIOTLB_SEGSIZE). > > > > > > > > > > > > In certain applications, the default value of IO_TLB_SEGSIZE > > > > > > (128) > > > > > > may > > > > > > not be sufficient for memory allocation, leading to runtime > > > > > > errors. > > > > > > By > > > > > > making this parameter configurable, users can adjust the > > > > > > segment > > > > > > size to > > > > > > better suit their specific use cases, improving flexibility and > > > > > > system > > > > > > stability. > > > > > > > > > > Could You elaborate a bit more what are those certain > > > > > applications > > > > > that > > > > > require increasing IO_TLB_SEGSIZE? I'm not against it, but such > > > > > change > > > > > should be well justified and described, while the above cover- > > > > > letter > > > > > doesn't provide anything more than is written in the patch > > > > > description. > > > > Thank you for your feedback, Marek. > > > > > > > > To provide more context, one specific application that requires > > > > increasing IO_TLB_SEGSIZE is the Hailo 8 PCIe AI card. This card > > > > uses > > > > dma_alloc_coherent to allocate descriptor lists, as seen in the > > > > Hailo > > > > driver implementation here: > > > > https://github.com/hailo-ai/hailort-drivers/blob/7161f9ee5918029bd4497f590003c2f87ec32507/linux/vdma/memory.c#L322 > > > > The maximum size (nslots) for these allocations can reach 160, > > > > which > > > > exceeds the current default value of IO_TLB_SEGSIZE (128). > > > > > > > > Since IO_TLB_SEGSIZE is defined as a constant in the kernel: > > > > > > > > `#define IO_TLB_SEGSIZE 128` > > > > > > > > > > > > this limitation causes swiotlb_search_pool_area, > > > > https://github.com/torvalds/linux/blame/v6.15-rc2/kernel/dma/swiotlb.c#L1085 > > > > , > > > > (or swiotlb_do_find_slots in older kernels) to fail when attempting > > > > to > > > > allocate contiguous physical memory (CMA). This results in runtime > > > > errors and prevents the Hailo 8 card from functioning correctly in > > > > certain configurations. > > > > > > Hmm, dma_alloc_coherent() should really not be trying to allocate > > > from > > > SWIOTLB in the first place - how is that happening? > > > > > > If you're using restricted DMA for a device which wants significant > > > coherent allocations, then it wants to have it's own shared-dma-pool > > > for > > > those *as well* as the restricted-dma-pool for bouncing streaming > > > DMA. > > > > > > Thanks, > > > Robin. > > > > Hi Robin, > > > > Regarding the specific Hailo Card case, the issue arises due > > to the capabilities of certain SoCs or CPUs. For example, many > > K3 SoCs lack an IOMMU, which is typically used to isolate the > > system against DMA-based attacks of external PCI devices. > > > > Taking the TI AM65 as an example, it doesn't have an IOMMU, but > > instead includes a Peripheral Virtualization Unit (PVU). The > > PVU provides functionality similar to an IOMMU and is used to > > isolate PCI devices from the Linux host, and the SWIOTLB is > > used to manp all DMA buffers from a static memory carve-out. > > And as I said, if you want to support general coherent allocations then you > should use part of that carveout for a regular coherent DMA pool. The > restricted pool is only intended for streaming DMA - swiotlb_alloc() is only > meant as a convenience fallback for the kind of devices which mostly do > streaming DMA but make one or two small coherent allocations from a suitable > context. It does not work for *all* valid usage of dma_alloc_attrs(), and if > you want to do this for arbitrary PCI devices then you almost certainly *do* > need to be able to support drivers which make allocations in atomic context. If they utilize dma_alloc_coherent and setup at boot-time those buffers then that does exactly the same thing as the coherent DMA pool. Albeit less flexible, but nonethless the same thing. That seems like a valid use-case, no?
On Fri, 2025-04-25 at 11:42 +0100, Robin Murphy wrote: > On 2025-04-25 6:32 am, Li, Hua Qian wrote: > > On Thu, 2025-04-24 at 13:58 +0100, Robin Murphy wrote: > > > On 24/04/2025 6:12 am, Li, Hua Qian wrote: > > > > On Tue, 2025-04-22 at 15:36 +0200, Marek Szyprowski wrote: > > > > > On 22.04.2025 08:37, huaqian.li@siemens.com wrote: > > > > > > From: Li Hua Qian <huaqian.li@siemens.com> > > > > > > > > > > > > This patchset introduces a change to make the > > > > > > IO_TLB_SEGSIZE > > > > > > parameter > > > > > > configurable via a new kernel configuration option > > > > > > (CONFIG_SWIOTLB_SEGSIZE). > > > > > > > > > > > > In certain applications, the default value of > > > > > > IO_TLB_SEGSIZE > > > > > > (128) > > > > > > may > > > > > > not be sufficient for memory allocation, leading to runtime > > > > > > errors. > > > > > > By > > > > > > making this parameter configurable, users can adjust the > > > > > > segment > > > > > > size to > > > > > > better suit their specific use cases, improving flexibility > > > > > > and > > > > > > system > > > > > > stability. > > > > > > > > > > Could You elaborate a bit more what are those certain > > > > > applications > > > > > that > > > > > require increasing IO_TLB_SEGSIZE? I'm not against it, but > > > > > such > > > > > change > > > > > should be well justified and described, while the above > > > > > cover- > > > > > letter > > > > > doesn't provide anything more than is written in the patch > > > > > description. > > > > Thank you for your feedback, Marek. > > > > > > > > To provide more context, one specific application that requires > > > > increasing IO_TLB_SEGSIZE is the Hailo 8 PCIe AI card. This > > > > card > > > > uses > > > > dma_alloc_coherent to allocate descriptor lists, as seen in the > > > > Hailo > > > > driver implementation here: > > > > https://github.com/hailo-ai/hailort-drivers/blob/7161f9ee5918029bd4497f590003c2f87ec32507/linux/vdma/memory.c#L322 > > > > The maximum size (nslots) for these allocations can reach 160, > > > > which > > > > exceeds the current default value of IO_TLB_SEGSIZE (128). > > > > > > > > Since IO_TLB_SEGSIZE is defined as a constant in the kernel: > > > > > > > > `#define IO_TLB_SEGSIZE 128` > > > > > > > > > > > > this limitation causes swiotlb_search_pool_area, > > > > https://github.com/torvalds/linux/blame/v6.15-rc2/kernel/dma/swiotlb.c#L1085 > > > > , > > > > (or swiotlb_do_find_slots in older kernels) to fail when > > > > attempting > > > > to > > > > allocate contiguous physical memory (CMA). This results in > > > > runtime > > > > errors and prevents the Hailo 8 card from functioning correctly > > > > in > > > > certain configurations. > > > > > > Hmm, dma_alloc_coherent() should really not be trying to allocate > > > from > > > SWIOTLB in the first place - how is that happening? > > > > > > If you're using restricted DMA for a device which wants > > > significant > > > coherent allocations, then it wants to have it's own shared-dma- > > > pool > > > for > > > those *as well* as the restricted-dma-pool for bouncing streaming > > > DMA. > > > > > > Thanks, > > > Robin. > > > > Hi Robin, > > > > Regarding the specific Hailo Card case, the issue arises due > > to the capabilities of certain SoCs or CPUs. For example, many > > K3 SoCs lack an IOMMU, which is typically used to isolate the > > system against DMA-based attacks of external PCI devices. > > > > Taking the TI AM65 as an example, it doesn't have an IOMMU, but > > instead includes a Peripheral Virtualization Unit (PVU). The > > PVU provides functionality similar to an IOMMU and is used to > > isolate PCI devices from the Linux host, and the SWIOTLB is > > used to manp all DMA buffers from a static memory carve-out. > > And as I said, if you want to support general coherent allocations > then > you should use part of that carveout for a regular coherent DMA pool. > The restricted pool is only intended for streaming DMA - > swiotlb_alloc() > is only meant as a convenience fallback for the kind of devices which > mostly do streaming DMA but make one or two small coherent > allocations > from a suitable context. It does not work for *all* valid usage of > dma_alloc_attrs(), and if you want to do this for arbitrary PCI > devices > then you almost certainly *do* need to be able to support drivers > which > make allocations in atomic context. > > Thanks, > Robin. Thank you for your detailed explanation, Robin. I understand your points and agree with your suggestions. Based on this, I will conclude this upstreaming patchset here. Thank you again for your guiidance and support. Best Regards, Li Hua Qian > > > You can find more details and background information here: > > https://lore.kernel.org/all/20250422061406.112539-1-huaqian.li@siemens.com/ > > > > > > > > > By making IO_TLB_SEGSIZE configurable via a kernel > > > > configuration > > > > option > > > > (CONFIG_SWIOTLB_SEGSIZE), users can adjust the segment size to > > > > accommodate such use cases. This change improves flexibility > > > > and > > > > ensures that systems can be tailored to meet the requirements > > > > of > > > > specific hardware, such as the Hailo 8 PCIe AI card, without > > > > requiring > > > > kernel source modifications. > > > > > > > > I hope this example clarifies the need for this change. Please > > > > let > > > > me > > > > know if further details or additional examples are required. > > > > > > > > Best Regards, > > > > Li Hua Qian > > > > > > > > > > > > > > > > Li Hua Qian (1): > > > > > > swiotlb: Make IO_TLB_SEGSIZE configurable > > > > > > > > > > > > include/linux/swiotlb.h | 2 +- > > > > > > kernel/dma/Kconfig | 7 +++++++ > > > > > > 2 files changed, 8 insertions(+), 1 deletion(-) > > > > > > > > > > > Best regards > > > > > > > > -- > > Hua Qian Li > > Siemens AG > > http://www.siemens.com/ > -- Hua Qian Li Siemens AG http://www.siemens.com/
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