Messages in this thread | | | Subject | Re: [PATCH v4 6/9] iommu/vt-d: Check whether device requires bounce buffer | From | Lu Baolu <> | Date | Wed, 12 Jun 2019 10:22:33 +0800 |
| |
Hi,
On 6/11/19 12:08 AM, Konrad Rzeszutek Wilk wrote: > On Mon, Jun 03, 2019 at 09:16:17AM +0800, Lu Baolu wrote: >> This adds a helper to check whether a device needs to use bounce >> buffer. It also provides a boot time option to disable the bounce >> buffer. Users can use this to prevent the iommu driver from using >> the bounce buffer for performance gain. >> >> Cc: Ashok Raj <ashok.raj@intel.com> Cc: Jacob Pan >> <jacob.jun.pan@linux.intel.com> Cc: Kevin Tian >> <kevin.tian@intel.com> Signed-off-by: Lu Baolu >> <baolu.lu@linux.intel.com> Tested-by: Xu Pengfei >> <pengfei.xu@intel.com> Tested-by: Mika Westerberg >> <mika.westerberg@intel.com> --- >> Documentation/admin-guide/kernel-parameters.txt | 5 +++++ >> drivers/iommu/intel-iommu.c | 6 ++++++ 2 files >> changed, 11 insertions(+) >> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt >> b/Documentation/admin-guide/kernel-parameters.txt index >> 138f6664b2e2..65685c6e53e4 100644 --- >> a/Documentation/admin-guide/kernel-parameters.txt +++ >> b/Documentation/admin-guide/kernel-parameters.txt @@ -1728,6 >> +1728,11 @@ Note that using this option lowers the security >> provided by tboot because it makes the system vulnerable to DMA >> attacks. + nobounce [Default off] + Do not use the bounce buffer >> for untrusted devices like + the Thunderbolt devices. This will >> treat the untrusted > > My brain has sometimes a hard time parsing 'Not' and 'un'. Could this > be: > > Disable bounce buffer for unstrusted devices ..? >
Fair enough.
> > And perhaps call it 'noswiotlb' ? Not everyone knows that SWIOTLB = > bounce buffer.
As I said in previous thread, swiotlb is not only used for BOUNCE_PAGE case, but also used by direct dma APIs. Will it cause confusion?
Anyway, I have no strong feeling to use 'nobounce' or 'noswiotlb'. It's a driver specific switch for debugging purpose. People suggested that we should move this switch into pci module, but I heard that it's more helpful to implement per-device switch for "trusted' or "untrusted". So I kept this untouched in this version.
> >> + devices as the trusted ones, hence might expose security + >> risks of DMA attacks. >> >> intel_idle.max_cstate= [KNL,HW,ACPI,X86] 0 disables intel_idle and >> fall back on acpi_idle. diff --git a/drivers/iommu/intel-iommu.c >> b/drivers/iommu/intel-iommu.c index 235837c50719..41439647f75d >> 100644 --- a/drivers/iommu/intel-iommu.c +++ >> b/drivers/iommu/intel-iommu.c @@ -371,6 +371,7 @@ static int >> dmar_forcedac; static int intel_iommu_strict; static int >> intel_iommu_superpage = 1; static int iommu_identity_mapping; >> +static int intel_no_bounce; > > intel_swiotlb_on = 1 ? > >> >> #define IDENTMAP_ALL 1 #define IDENTMAP_GFX 2 @@ -384,6 +385,8 @@ >> EXPORT_SYMBOL_GPL(intel_iommu_gfx_mapped); static >> DEFINE_SPINLOCK(device_domain_lock); static >> LIST_HEAD(device_domain_list); >> >> +#define device_needs_bounce(d) (!intel_no_bounce && >> dev_is_untrusted(d)) + /* * Iterate over elements in >> device_domain_list and call the specified * callback @fn against >> each element. @@ -466,6 +469,9 @@ static int __init >> intel_iommu_setup(char *str) printk(KERN_INFO "Intel-IOMMU: not >> forcing on after tboot. This could expose security risk for >> tboot\n"); intel_iommu_tboot_noforce = 1; + } else if >> (!strncmp(str, "nobounce", 8)) { + pr_info("Intel-IOMMU: No >> bounce buffer. This could expose security risks of DMA >> attacks\n"); > > Again, Intel-IOMMU: No SWIOTLB. T.. blah blah' > > Asking for this as doing 'dmesg | grep SWIOTLB' will expose nicely > all the SWIOTLB invocations..
Yes. Will refine this.
Best regards, Baolu
| |