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x86/pci-dma: remove the experimental forcesac boot option

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Limiting the dma mask to avoid PCI (pre-PCIe) DAC cycles while paying
the huge overhead of an IOMMU is rather pointless, and this seriously
gets in the way of dma mapping work.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Christoph Hellwig 2018-04-27 09:13:24 +02:00
parent 84564d1c76
commit 06e9552f5f
5 changed files with 6 additions and 30 deletions
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1
Documentation/admin-guide/kernel-parameters.txt
View File

@ -1705,7 +1705,6 @@
nopanic
merge
nomerge
forcesac
soft
pt [x86, IA-64]
nobypass [PPC/POWERNV]

4
Documentation/x86/x86_64/boot-options.txt
View File

@ -208,7 +208,7 @@ IOMMU (input/output memory management unit)
Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
[,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
[,memaper[=<order>]][,merge][,fullflush][,nomerge]
[,noaperture][,calgary]
General iommu options:
@ -235,8 +235,6 @@ IOMMU (input/output memory management unit)
(experimental).
nomerge Don't do scatter-gather (SG) merging.
noaperture Ask the IOMMU not to touch the aperture for AGP.
forcesac Force single-address cycle (SAC) mode for masks <40bits
(experimental).
noagp Don't initialize the AGP driver and use full aperture.
allowdac Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
DAC is used with 32-bit PCI to push a 64-bit address in

21
arch/x86/kernel/pci-dma.c
View File

@ -20,8 +20,6 @@ static int forbid_dac __read_mostly;
const struct dma_map_ops *dma_ops = &dma_direct_ops;
EXPORT_SYMBOL(dma_ops);
static int iommu_sac_force __read_mostly;
#ifdef CONFIG_IOMMU_DEBUG
int panic_on_overflow __read_mostly = 1;
int force_iommu __read_mostly = 1;
@ -122,7 +120,7 @@ static __init int iommu_setup(char *p)
if (!strncmp(p, "nomerge", 7))
iommu_merge = 0;
if (!strncmp(p, "forcesac", 8))
iommu_sac_force = 1;
pr_warn("forcesac option ignored.\n");
if (!strncmp(p, "allowdac", 8))
forbid_dac = 0;
if (!strncmp(p, "nodac", 5))
@ -162,23 +160,6 @@ int arch_dma_supported(struct device *dev, u64 mask)
}
#endif
/* Tell the device to use SAC when IOMMU force is on. This
allows the driver to use cheaper accesses in some cases.
Problem with this is that if we overflow the IOMMU area and
return DAC as fallback address the device may not handle it
correctly.
As a special case some controllers have a 39bit address
mode that is as efficient as 32bit (aic79xx). Don't force
SAC for these. Assume all masks <= 40 bits are of this
type. Normally this doesn't make any difference, but gives
more gentle handling of IOMMU overflow. */
if (iommu_sac_force && (mask >= DMA_BIT_MASK(40))) {
dev_info(dev, "Force SAC with mask %Lx\n", mask);
return 0;
}
return 1;
}
EXPORT_SYMBOL(arch_dma_supported);

5
drivers/net/ethernet/sfc/efx.c
View File

@ -1289,9 +1289,8 @@ static int efx_init_io(struct efx_nic *efx)
pci_set_master(pci_dev);
/* Set the PCI DMA mask. Try all possibilities from our
* genuine mask down to 32 bits, because some architectures
* (e.g. x86_64 with iommu_sac_force set) will allow 40 bit
/* Set the PCI DMA mask. Try all possibilities from our genuine mask
* down to 32 bits, because some architectures will allow 40 bit
* masks event though they reject 46 bit masks.
*/
while (dma_mask > 0x7fffffffUL) {

5
drivers/net/ethernet/sfc/falcon/efx.c
View File

@ -1242,9 +1242,8 @@ static int ef4_init_io(struct ef4_nic *efx)
pci_set_master(pci_dev);
/* Set the PCI DMA mask. Try all possibilities from our
* genuine mask down to 32 bits, because some architectures
* (e.g. x86_64 with iommu_sac_force set) will allow 40 bit
/* Set the PCI DMA mask. Try all possibilities from our genuine mask
* down to 32 bits, because some architectures will allow 40 bit
* masks event though they reject 46 bit masks.
*/
while (dma_mask > 0x7fffffffUL) {