[PATCH 1/1] x86/iommu: fix incorrect bit operations in setting values

Li, ZhenHua zhen-hual at hp.com
Thu Nov 13 17:29:51 PST 2014


On 11/13/2014 09:37 PM, Baoquan He wrote:
> On 11/13/14 at 05:06pm, Li, ZhenHua wrote:
>> Minfei,
>> Thanks for your testing.
>> On my system, I got error messages:
>>
>> [    8.019096] usb usb2: New USB device strings: Mfr=3, Product=2,
>> SerialNumber=1
>> [    8.019617] dmar: DRHD: handling fault status reg 102
>> [    8.019621] dmar: DMAR:[DMA Read] Request device [01:00.0] fault
>> addr fff6a000
>> [    8.019621] DMAR:[fault reason 06] PTE Read access is not set
>> [    8.019627] dmar: DRHD: handling fault status reg 202
>> [    8.019631] dmar: DMAR:[DMA Read] Request device [21:00.0] fault
>> addr fff6a000
>> [    8.019631] DMAR:[fault reason 06] PTE Read access is not set
>> [    8.019638] dmar: DRHD: handling fault status reg 202
>> [    8.019641] dmar: DMAR:[DMA Read] Request device [41:00.0] fault
>> addr fff6a000
>> [    8.019641] DMAR:[fault reason 06] PTE Read access is not set
>> [    8.019647] dmar: DRHD: handling fault status reg 202
>> [    8.019651] dmar: DMAR:[DMA Read] Request device [61:00.0] fault
>> addr fff6a000
>> [    8.019651] DMAR:[fault reason 06] PTE Read access is not set
>>
>> And this patch can fix this.
>>
>>
>> The reason you do not get error messages may be there is no ongoing DMA
>> request on your PCI devices when kdump kernel boots, I am not sure of
>> this.
>
> I think Minfei means he applied this patch, so no error message is got.
> The patches he listed includes this one:
>
> 0006-x86-iommu-fix-incorrect-bit-operations-in-setting-va.patch
Oh, thank you very much for your correction.
>
> Hi Zhenhua,
>
> Below is abstracted from Joerg's comments which he and David discussed
> and get to this conclusion. So the 1st step is the same as your patches,
> how do you think the 2nd step?
>
> 	1. If the VT-d driver finds the IOMMU enabled, it reuses its
>             root-context table. This way the IOMMU must not be disabled
>             and re-enabled, eliminating the race we have now.
>             Other data structures like the context-entries are copied
>             over from the old kernel.  We basically keep all mappings
>             from the old kernel, allowing any in-flight DMA to succeed.
>             No memory or disk data corruption.
>             The issue here is, that we modify data from the old kernel
>             which is about to be dumped. But there are ways to work
>             around that.
>
>          2. When a device driver issues the first dma_map command for a
>             device, we assign a new and empty page-table, thus removing
>             all mappings from the old kernel for the device.
>             Rationale is, that at this point the device driver should
>             have reset the device to a point where all in-flight DMA is
>             canceled.
>
1st step shows we should NOT disable the iommu when it is already 
enabled. But current code does disable-enable. So there is still works 
to do.

I think step 2 is necessary, because when the driver initializes, the 
device need a new map, and the old data from the old kernel can not be 
used for the new driver.

Now I am trying to implement these ideas.

> Thanks
> Baoquan
>
>>
>> Zhenhua
>> On 11/12/2014 07:28 PM, Minfei Huang wrote:
>>> The kdump starts 2nd kernel without any error message when I use
>>> 3.18.0-rc4 merged last 6 patchs. The following is the message which 2nd
>>> kernel prints during booting.
>>>
>>> Patchset:
>>> 	0001-iommu-vt-d-Update-iommu_attach_domain-and-its-caller.patch
>>> 	0002-iommu-vt-d-Items-required-for-kdump.patch
>>> 	0003-iommu-vt-d-data-types-and-functions-used-for-kdump.patch
>>> 	0004-iommu-vt-d-Add-domain-id-functions.patch
>>> 	0005-iommu-vt-d-enable-kdump-support-in-iommu-module.patch
>>> 	0006-x86-iommu-fix-incorrect-bit-operations-in-setting-va.patch
>>>
>>> log:
>>> [    1.689604] IOMMU intel_iommu_in_crashdump = true
>>> [    1.694310] IOMMU Skip disabling iommu hardware translations
>>> [    1.699987] DMAR: No ATSR found
>>> [    1.703151] IOMMU Copying translate tables from panicked kernel
>>> [    1.710786] IOMMU: root_new_virt:0xffff8800296ec000 phys:0x0000296ec000
>>> [    1.717401] IOMMU:0 Domain ids from panicked kernel:
>>> [    1.722364] DID did:13(0x000d)
>>> [    1.725424] DID did:12(0x000c)
>>> [    1.728482] DID did:11(0x000b)
>>> [    1.731542] DID did:10(0x000a)
>>> [    1.734603] DID did:6(0x0006)
>>> [    1.737574] DID did:7(0x0007)
>>> [    1.740549] DID did:5(0x0005)
>>> [    1.743522] DID did:9(0x0009)
>>> [    1.746495] DID did:8(0x0008)
>>> [    1.749467] DID did:4(0x0004)
>>> [    1.752439] DID did:3(0x0003)
>>> [    1.755413] DID did:2(0x0002)
>>> [    1.758385] DID did:0(0x0000)
>>> [    1.761357] DID did:1(0x0001)
>>> [    1.764331] ----------------------------------------
>>> [    1.769302] IOMMU 0 0xfed50000: using Queued invalidation
>>>
>>> On 11/05/14 at 03:30pm, Li, Zhen-Hua wrote:
>>>> The function context_set_address_root() and set_root_value are setting new
>>>> address in a wrong way, and this patch is trying to fix this problem.
>>>>
>>>> According to Intel Vt-d specs(Feb 2011, Revision 1.3), Chapter 9.1 and 9.2,
>>>> field ctp in root entry is using bits 12:63, field asr in context entry is
>>>> using bits 12:63.
>>>>
>>>> To set these fields, the following functions are used:
>>>> static inline void context_set_address_root(struct context_entry *context,
>>>>          unsigned long value);
>>>> and
>>>> static inline void set_root_value(struct root_entry *root, unsigned long value)
>>>>
>>>> But they are using an invalid method to set these fields, in current code, only
>>>> a '|' operator is used to set it. This will not set the asr to the expected
>>>> value if it has an old value.
>>>>
>>>> For example:
>>>> Before calling this function,
>>>> 	context->lo = 0x3456789012111;
>>>> 	value = 0x123456789abcef12;
>>>>
>>>> After we call context_set_address_root(context, value), expected result is
>>>> 	context->lo == 0x123456789abce111;
>>>>
>>>> But the actual result is:
>>>> 	context->lo == 0x1237577f9bbde111;
>>>>
>>>> So we need to clear bits 12:63 before setting the new value, this will fix
>>>> this problem.
>>>>
>>>> Signed-off-by: Li, Zhen-Hua <zhen-hual at hp.com>
>>>> ---
>>>>   drivers/iommu/intel-iommu.c | 2 ++
>>>>   1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>>>> index a27d6cb..11ac47b 100644
>>>> --- a/drivers/iommu/intel-iommu.c
>>>> +++ b/drivers/iommu/intel-iommu.c
>>>> @@ -195,6 +195,7 @@ static inline void set_root_present(struct root_entry *root)
>>>>   }
>>>>   static inline void set_root_value(struct root_entry *root, unsigned long value)
>>>>   {
>>>> +	root->val &= ~VTD_PAGE_MASK;
>>>>   	root->val |= value & VTD_PAGE_MASK;
>>>>   }
>>>>
>>>> @@ -247,6 +248,7 @@ static inline void context_set_translation_type(struct context_entry *context,
>>>>   static inline void context_set_address_root(struct context_entry *context,
>>>>   					    unsigned long value)
>>>>   {
>>>> +	context->lo &= ~VTD_PAGE_MASK;
>>>>   	context->lo |= value & VTD_PAGE_MASK;
>>>>   }
>>>>
>>>> --
>>>> 2.0.0-rc0
>>>>
>>>> --
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>>
>>
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