Re: [RFC] iommu/vt-d: set default value of INTEL_IOMMU_FLOPPY_WA to n
From: Harshit Mogalapalli
Date: Wed Nov 09 2022 - 08:56:02 EST
On 09/11/22 6:56 pm, Robin Murphy wrote:
On 09/11/2022 12:16 pm, Harshit Mogalapalli wrote:
On 09/11/22 12:35 pm, Baolu Lu wrote:
On 2022/11/8 20:58, Harshit Mogalapalli wrote:
It is likely that modern intel motherboard will not ship with a
floppy connection anymore, so let us disable it by default, as it
gets turned on when we do a make defconfig.
Suggested-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
---
drivers/iommu/intel/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
index b7dff5092fd2..c783ae85ca9b 100644
--- a/drivers/iommu/intel/Kconfig
+++ b/drivers/iommu/intel/Kconfig
@@ -76,7 +76,7 @@ config INTEL_IOMMU_BROKEN_GFX_WA
option is removed in the 2.6.32 kernel.
config INTEL_IOMMU_FLOPPY_WA
- def_bool y
+ def_bool n
depends on X86
help
Floppy disk drivers are known to bypass DMA API calls
Nobody selects or depends on this. How about removing this bool? Only
less than 10 lines of code are impacted and are not in any performance
path.
diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
index b7dff5092fd2..5e077d1c5f5d 100644
--- a/drivers/iommu/intel/Kconfig
+++ b/drivers/iommu/intel/Kconfig
@@ -75,15 +75,6 @@ config INTEL_IOMMU_BROKEN_GFX_WA
to use physical addresses for DMA, at least until this
option is removed in the 2.6.32 kernel.
-config INTEL_IOMMU_FLOPPY_WA
- def_bool y
- depends on X86
- help
- Floppy disk drivers are known to bypass DMA API calls
- thereby failing to work when IOMMU is enabled. This
- workaround will setup a 1:1 mapping for the first
- 16MiB to make floppy (an ISA device) work.
-
config INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
bool "Enable Intel IOMMU scalable mode by default"
default y
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 48cdcd0a5cf3..22801850f339 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4567,7 +4567,6 @@ static void intel_iommu_get_resv_regions(struct
device *device,
}
rcu_read_unlock();
-#ifdef CONFIG_INTEL_IOMMU_FLOPPY_WA
if (dev_is_pci(device)) {
struct pci_dev *pdev = to_pci_dev(device);
@@ -4579,7 +4578,6 @@ static void intel_iommu_get_resv_regions(struct
device *device,
list_add_tail(®->list, head);
}
}
-#endif /* CONFIG_INTEL_IOMMU_FLOPPY_WA */
reg = iommu_alloc_resv_region(IOAPIC_RANGE_START,
IOAPIC_RANGE_END - IOAPIC_RANGE_START + 1,
Hi Baolu,
I have a question:
Shouldn't we remove the code between ifdef-endif statements?
Hi Baolu and Robin,
No, machines with floppy drives may be uncommon, but almost certainly
some are still in use and being updated with new kernels, so we should
continue to support them.
Thanks a lot for explaining.
I misunderstood the code, I thought when we are removing ifdef-endif
statement, the code inside(within ifdef-endif) becomes redundant, thanks
for correcting me.
Do you have any practical issues with the ISA reserved region being
present, or is the only motivation here to save a few bytes of code when
it won't be needed? In the latter case, making it "def_bool BLK_DEV_FD"
might be sensible.
No practical issues seen.
(For the original patch, note that "def_bool n" is always a bit
redundant since plain "bool" implicitly defaults to "n" anyway)
Okay.
How about Baolu's version of the patch, where we are removing the CONFIG
item from Kconfig and ifdef statement from the code in iommu.c?
Thanks,
Harshit
Thanks,
Robin.
I mean something like this:
diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
index b7dff5092fd2..5e077d1c5f5d 100644
--- a/drivers/iommu/intel/Kconfig
+++ b/drivers/iommu/intel/Kconfig
@@ -75,15 +75,6 @@ config INTEL_IOMMU_BROKEN_GFX_WA
to use physical addresses for DMA, at least until this
option is removed in the 2.6.32 kernel.
-config INTEL_IOMMU_FLOPPY_WA
- def_bool y
- depends on X86
- help
- Floppy disk drivers are known to bypass DMA API calls
- thereby failing to work when IOMMU is enabled. This
- workaround will setup a 1:1 mapping for the first
- 16MiB to make floppy (an ISA device) work.
-
config INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
bool "Enable Intel IOMMU scalable mode by default"
default y
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 48cdcd0a5cf3..2c416ad3204e 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4567,20 +4567,6 @@ static void intel_iommu_get_resv_regions(struct
device *device,
}
rcu_read_unlock();
-#ifdef CONFIG_INTEL_IOMMU_FLOPPY_WA
- if (dev_is_pci(device)) {
- struct pci_dev *pdev = to_pci_dev(device);
-
- if ((pdev->class >> 8) == PCI_CLASS_BRIDGE_ISA) {
- reg = iommu_alloc_resv_region(0, 1UL << 24, prot,
- IOMMU_RESV_DIRECT_RELAXABLE,
- GFP_KERNEL);
- if (reg)
- list_add_tail(®->list, head);
- }
- }
-#endif /* CONFIG_INTEL_IOMMU_FLOPPY_WA */
-
reg = iommu_alloc_resv_region(IOAPIC_RANGE_START,
IOAPIC_RANGE_END -
IOAPIC_RANGE_START + 1,
0, IOMMU_RESV_MSI, GFP_KERNEL);
This code is introduced in Commit d850c2ee5fe2 ("iommu/vt-d: Expose
ISA direct mapping region via iommu_get_resv_regions")
If others don't have an objection I can send a patch with the above diff.
Note: I am unsure about the code internals.
Thanks,
Harshit
Best regards,
baolu