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Message-Id: <20180525143512.1466-6-hch@lst.de>
Date: Fri, 25 May 2018 16:35:10 +0200
From: Christoph Hellwig <hch@....de>
To: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Tony Luck <tony.luck@...el.com>,
Fenghua Yu <fenghua.yu@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: x86@...nel.org, iommu@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
netdev@...r.kernel.org
Subject: [PATCH 5/7] x86: remove the experimental forcesac boot option
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@....de>
---
.../admin-guide/kernel-parameters.txt | 1 -
Documentation/x86/x86_64/boot-options.txt | 4 +---
arch/x86/kernel/pci-dma.c | 21 +------------------
drivers/net/ethernet/sfc/efx.c | 5 ++---
drivers/net/ethernet/sfc/falcon/efx.c | 5 ++---
5 files changed, 6 insertions(+), 30 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f2040d46f095..cc0ac035b8fe 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1705,7 +1705,6 @@
nopanic
merge
nomerge
- forcesac
soft
pt [x86, IA-64]
nobypass [PPC/POWERNV]
diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt
index 153b3a57fba2..341588ec4e29 100644
--- a/Documentation/x86/x86_64/boot-options.txt
+++ b/Documentation/x86/x86_64/boot-options.txt
@@ -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
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index 77625b60a510..91dff954b745 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -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;
@@ -125,7 +123,7 @@ 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))
@@ -165,23 +163,6 @@ 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);
diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index a4ebd8715494..661828e8fdcf 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -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) {
diff --git a/drivers/net/ethernet/sfc/falcon/efx.c b/drivers/net/ethernet/sfc/falcon/efx.c
index 3d6c91e96589..dd5530a4f8c8 100644
--- a/drivers/net/ethernet/sfc/falcon/efx.c
+++ b/drivers/net/ethernet/sfc/falcon/efx.c
@@ -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) {
--
2.17.0
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