Strictness has the semantic of being a per-domain property. This is why iommu_get_dma_strict() takes a "struct iommu_domain" as a parameter. Let's add knowledge to the "struct iommu_domain" so we can know whether we'd like each domain to be strict. In this patch nothing sets the per-domain strictness, it just paves the way for future patches to do so. Prior to this patch we could only affect strictness at a global level. We'll still honor the global strictness level if it has been explicitly set and it's stricter than the one requested per-domain. NOTE: it's even more obvious that iommu_set_dma_strict() and iommu_get_dma_strict() are non-symmetric after this change. However, they have always been asymmetric by design [0]. The function iommu_get_dma_strict() should now make it super obvious where strictness comes from and who overides who. Though the function changed a bunch to make the logic clearer, the only two new rules should be: * Devices can force strictness for themselves, overriding the cmdline "iommu.strict=0" or a call to iommu_set_dma_strict(false)). * Devices can request non-strictness for themselves, assuming there was no cmdline "iommu.strict=1" or a call to iommu_set_dma_strict(true). [0] https://lore.kernel.org/r/a023af85-5060-0a3c-4648-b00f8b8c0430@xxxxxxx/ Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> --- This patch clearly will cause conflicts if John Garry's patches [1] land before it. It shouldn't be too hard to rebase, though. Essentially with John's patches it'll be impossible for what's called `cmdline_dma_strict` in my patch to be "default". It'll probably make sense to rearrange the logic/names a bit though just to make things clearer. [1] https://lore.kernel.org/r/1624016058-189713-1-git-send-email-john.garry@xxxxxxxxxx/ Changes in v2: - No longer based on changes adding strictness to "struct device" - Updated kernel-parameters docs. .../admin-guide/kernel-parameters.txt | 5 ++- drivers/iommu/iommu.c | 43 +++++++++++++++---- include/linux/iommu.h | 7 +++ 3 files changed, 45 insertions(+), 10 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index cb89dbdedc46..7675fd79f9a9 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1995,9 +1995,12 @@ throughput at the cost of reduced device isolation. Will fall back to strict mode if not supported by the relevant IOMMU driver. - 1 - Strict mode (default). + 1 - Strict mode. DMA unmap operations invalidate IOMMU hardware TLBs synchronously. + NOTE: if "iommu.strict" is not specified in the command + line then it's up to the system to try to determine the + proper strictness. iommu.passthrough= [ARM64, X86] Configure DMA to bypass the IOMMU by default. diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index 808ab70d5df5..7943d2105b2f 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -29,7 +29,8 @@ static struct kset *iommu_group_kset; static DEFINE_IDA(iommu_group_ida); static unsigned int iommu_def_domain_type __read_mostly; -static bool iommu_dma_strict __read_mostly = true; +static enum iommu_strictness cmdline_dma_strict __read_mostly; +static enum iommu_strictness driver_dma_strict __read_mostly; static u32 iommu_cmd_line __read_mostly; struct iommu_group { @@ -69,7 +70,6 @@ static const char * const iommu_group_resv_type_string[] = { }; #define IOMMU_CMD_LINE_DMA_API BIT(0) -#define IOMMU_CMD_LINE_STRICT BIT(1) static int iommu_alloc_default_domain(struct iommu_group *group, struct device *dev); @@ -334,27 +334,52 @@ static int __init iommu_set_def_domain_type(char *str) } early_param("iommu.passthrough", iommu_set_def_domain_type); +static inline enum iommu_strictness bool_to_strictness(bool strict) +{ + return strict ? IOMMU_STRICT : IOMMU_NOT_STRICT; +} + static int __init iommu_dma_setup(char *str) { - int ret = kstrtobool(str, &iommu_dma_strict); + bool strict; + int ret = kstrtobool(str, &strict); if (!ret) - iommu_cmd_line |= IOMMU_CMD_LINE_STRICT; + cmdline_dma_strict = bool_to_strictness(strict); return ret; } early_param("iommu.strict", iommu_dma_setup); void iommu_set_dma_strict(bool strict) { - if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT)) - iommu_dma_strict = strict; + /* + * Valid transitions: + * - DEFAULT -> NON_STRICT + * - DEFAULT -> STRICT + * - NON_STRICT -> STRICT + * + * Everything else is ignored. + */ + if (driver_dma_strict != IOMMU_STRICT) + driver_dma_strict = bool_to_strictness(strict); } bool iommu_get_dma_strict(struct iommu_domain *domain) { - /* only allow lazy flushing for DMA domains */ - if (domain->type == IOMMU_DOMAIN_DMA) - return iommu_dma_strict; + /* Non-DMA domains or anyone forcing it to strict makes it strict */ + if (domain->type != IOMMU_DOMAIN_DMA || + cmdline_dma_strict == IOMMU_STRICT || + driver_dma_strict == IOMMU_STRICT || + domain->strictness == IOMMU_STRICT) + return true; + + /* Anyone requesting non-strict (if no forces) makes it non-strict */ + if (cmdline_dma_strict == IOMMU_NOT_STRICT || + driver_dma_strict == IOMMU_NOT_STRICT || + domain->strictness == IOMMU_NOT_STRICT) + return false; + + /* Nobody said anything, so it's strict by default */ return true; } EXPORT_SYMBOL_GPL(iommu_get_dma_strict); diff --git a/include/linux/iommu.h b/include/linux/iommu.h index 32d448050bf7..2e172059c931 100644 --- a/include/linux/iommu.h +++ b/include/linux/iommu.h @@ -79,8 +79,15 @@ struct iommu_domain_geometry { #define IOMMU_DOMAIN_DMA (__IOMMU_DOMAIN_PAGING | \ __IOMMU_DOMAIN_DMA_API) +enum iommu_strictness { + IOMMU_DEFAULT_STRICTNESS = 0, /* zero-init ends up at default */ + IOMMU_NOT_STRICT, + IOMMU_STRICT, +}; + struct iommu_domain { unsigned type; + enum iommu_strictness strictness; const struct iommu_ops *ops; unsigned long pgsize_bitmap; /* Bitmap of page sizes in use */ iommu_fault_handler_t handler; -- 2.32.0.93.g670b81a890-goog
