On 12/04/2019 11:26, John Garry wrote:
On 09/04/2019 13:53, Zhen Lei wrote:
Currently the IOMMU dma contains 3 modes: passthrough, lazy, strict. The
passthrough mode bypass the IOMMU, the lazy mode defer the invalidation
of hardware TLBs, and the strict mode invalidate IOMMU hardware TLBs
synchronously. The three modes are mutually exclusive. But the current
boot options are confused, such as: iommu.passthrough and iommu.strict,
because they are no good to be coexist. So add iommu.dma_mode.
Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 19 ++++++++
drivers/iommu/iommu.c | 59
++++++++++++++++++++-----
include/linux/iommu.h | 5 +++
3 files changed, 71 insertions(+), 12 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb64470d..f7766f8ac8b9084 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1811,6 +1811,25 @@
1 - Bypass the IOMMU for DMA.
unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
+ iommu.dma_mode= Configure default dma mode. if unset, use the value
+ of CONFIG_IOMMU_DEFAULT_PASSTHROUGH to determine
+ passthrough or not.
To me, for unset it's unclear what we default to. So if unset and also
CONFIG_IOMMU_DEFAULT_PASSTHROUGH is not set, do we get lazy or strict
mode? (note: I'm ignoring backwards compatibility and interaction of
iommu.strict and .passthorugh also, more below).
Could we considering introducing config DEFAULT_IOMMU_DMA_MODE, similar
to DEFAULT_IOSCHED?
Yes, what I was suggesting was specifically refactoring the Kconfig
options into a single choice that controls the default (i.e. no command
line option provided) behaviour. AFAICS it should be fairly
straightforward to maintain the existing "strict" and "passthrough"
options (and legacy arch-specific versions thereof) to override that
default without introducing yet another command-line option, which I
think we should avoid if possible.
+ Note: For historical reasons, ARM64/S390/PPC/X86 have
+ their specific options. Currently, only ARM64 support
+ this boot option, and hope other ARCHs to use this as
+ generic boot option.
+ passthrough
+ Configure DMA to bypass the IOMMU by default.
+ lazy
+ Request that DMA unmap operations use deferred
+ invalidation of hardware TLBs, for increased
+ throughput at the cost of reduced device isolation.
+ Will fall back to strict mode if not supported by
+ the relevant IOMMU driver.
+ strict
+ DMA unmap operations invalidate IOMMU hardware TLBs
+ synchronously.
+
io7= [HW] IO7 for Marvel based alpha systems
See comment before marvel_specify_io7 in
arch/alpha/kernel/core_marvel.c.
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 109de67d5d727c2..df1ce8e22385b48 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -38,12 +38,13 @@
static struct kset *iommu_group_kset;
static DEFINE_IDA(iommu_group_ida);
+
#ifdef CONFIG_IOMMU_DEFAULT_PASSTHROUGH
-static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY;
+#define IOMMU_DEFAULT_DMA_MODE IOMMU_DMA_MODE_PASSTHROUGH
#else
-static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
+#define IOMMU_DEFAULT_DMA_MODE IOMMU_DMA_MODE_STRICT
#endif
-static bool iommu_dma_strict __read_mostly = true;
+static int iommu_default_dma_mode __read_mostly =
IOMMU_DEFAULT_DMA_MODE;
struct iommu_callback_data {
const struct iommu_ops *ops;
@@ -147,20 +148,51 @@ static int __init iommu_set_def_domain_type(char
*str)
int ret;
ret = kstrtobool(str, &pt);
- if (ret)
- return ret;
+ if (!ret && pt)
+ iommu_default_dma_mode = IOMMU_DMA_MODE_PASSTHROUGH;
- iommu_def_domain_type = pt ? IOMMU_DOMAIN_IDENTITY :
IOMMU_DOMAIN_DMA;
- return 0;
+ return ret;
}
early_param("iommu.passthrough", iommu_set_def_domain_type);
static int __init iommu_dma_setup(char *str)
{
- return kstrtobool(str, &iommu_dma_strict);
+ bool strict;
+ int ret;
+
+ ret = kstrtobool(str, &strict);
+ if (!ret)
+ iommu_default_dma_mode = strict ?
+ IOMMU_DMA_MODE_STRICT : IOMMU_DMA_MODE_LAZY;
+
+ return ret;
}
early_param("iommu.strict", iommu_dma_setup);
+static int __init iommu_dma_mode_setup(char *str)
+{
+ if (!str)
+ goto fail;
+
+ if (!strncmp(str, "passthrough", 11))
+ iommu_default_dma_mode = IOMMU_DMA_MODE_PASSTHROUGH;
+ else if (!strncmp(str, "lazy", 4))
+ iommu_default_dma_mode = IOMMU_DMA_MODE_LAZY;
+ else if (!strncmp(str, "strict", 6))
+ iommu_default_dma_mode = IOMMU_DMA_MODE_STRICT;
+ else
+ goto fail;
+
+ pr_info("Force dma mode to be %d\n", iommu_default_dma_mode);
What happens if the cmdline option iommu.dma_mode is passed multiple
times? We get mutliple - possibily conflicting - prints, right?
Indeed; we ended up removing such prints for the existing options here,
specifically because multiple messages seemed more likely to be
confusing than useful.
And do we need to have backwards compatibility, such that the setting
for iommu.strict or iommu.passthrough trumps iommu.dma_mode, regardless
of order?
As above I think it would be preferable to just keep using the existing
options anyway. The current behaviour works out as:
iommu.passthrough | Y | N
iommu.strict | x | Y N
------------------|-------------|---------|--------
MODE | PASSTHROUGH | STRICT | LAZY
which seems intuitive enough that a specific dma_mode option doesn't add
much value, and would more likely just overcomplicate things for users
as well as our implementation.
Robin.
+
+ return 0;
+
+fail:
+ pr_debug("Boot option iommu.dma_mode is incorrect, ignored\n");
+ return -EINVAL;
+}
+early_param("iommu.dma_mode", iommu_dma_mode_setup);
+
static ssize_t iommu_group_attr_show(struct kobject *kobj,
struct attribute *__attr, char *buf)
{
@@ -1102,14 +1134,17 @@ struct iommu_group
*iommu_group_get_for_dev(struct device *dev)
*/
if (!group->default_domain) {
struct iommu_domain *dom;
+ int def_domain_type =
+ (iommu_default_dma_mode == IOMMU_DMA_MODE_PASSTHROUGH)
+ ? IOMMU_DOMAIN_IDENTITY : IOMMU_DOMAIN_DMA;
- dom = __iommu_domain_alloc(dev->bus, iommu_def_domain_type);
- if (!dom && iommu_def_domain_type != IOMMU_DOMAIN_DMA) {
+ dom = __iommu_domain_alloc(dev->bus, def_domain_type);
+ if (!dom && def_domain_type != IOMMU_DOMAIN_DMA) {
dom = __iommu_domain_alloc(dev->bus, IOMMU_DOMAIN_DMA);
if (dom) {
dev_warn(dev,
"failed to allocate default IOMMU domain of type
%u; falling back to IOMMU_DOMAIN_DMA",
- iommu_def_domain_type);
+ def_domain_type);
}
}
@@ -1117,7 +1152,7 @@ struct iommu_group
*iommu_group_get_for_dev(struct device *dev)
if (!group->domain)
group->domain = dom;
- if (dom && !iommu_dma_strict) {
+ if (dom && (iommu_default_dma_mode == IOMMU_DMA_MODE_LAZY)) {
int attr = 1;
iommu_domain_set_attr(dom,
DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ffbbc7e39ceeba3..c3f4e3416176496 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -42,6 +42,11 @@
*/
#define IOMMU_PRIV (1 << 5)
+
+#define IOMMU_DMA_MODE_STRICT 0x0
+#define IOMMU_DMA_MODE_LAZY 0x1
+#define IOMMU_DMA_MODE_PASSTHROUGH 0x2
+
struct iommu_ops;
struct iommu_group;
struct bus_type;
