Re: [PATCH V3 1/5] Swiotlb: Add Swiotlb bounce buffer remap function for HV IVM

Tom Lendacky
2021-12-03T20:07:06Z

On 12/3/21 1:11 PM, Tom Lendacky wrote:
> On 12/3/21 5:20 AM, Tianyu Lan wrote:
>> On 12/2/2021 10:42 PM, Tom Lendacky wrote:
>>> On 12/1/21 10:02 AM, Tianyu Lan wrote:
>>>> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
>>>>
>>>> In Isolation VM with AMD SEV, bounce buffer needs to be accessed via
>>>> extra address space which is above shared_gpa_boundary (E.G 39 bit
>>>> address line) reported by Hyper-V CPUID ISOLATION_CONFIG. The access
>>>> physical address will be original physical address + shared_gpa_boundary.
>>>> The shared_gpa_boundary in the AMD SEV SNP spec is called virtual top of
>>>> memory(vTOM). Memory addresses below vTOM are automatically treated as
>>>> private while memory above vTOM is treated as shared.
>>>>
>>>> Expose swiotlb_unencrypted_base for platforms to set unencrypted
>>>> memory base offset and platform calls swiotlb_update_mem_attributes()
>>>> to remap swiotlb mem to unencrypted address space. memremap() can
>>>> not be called in the early stage and so put remapping code into
>>>> swiotlb_update_mem_attributes(). Store remap address and use it to copy
>>>> data from/to swiotlb bounce buffer.
>>>>
>>>> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
>>>
>>> This patch results in the following stack trace during a bare-metal boot
>>> on my EPYC system with SME active (e.g. mem_encrypt=on):
>>>
>>> [    0.123932] BUG: Bad page state in process swapper  pfn:108001
>>> [    0.123942] page:(____ptrval____) refcount:0 mapcount:-128
>>> mapping:0000000000000000 index:0x0 pfn:0x108001
>>> [    0.123946] flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff)
>>> [    0.123952] raw: 0017ffffc0000000 ffff88904f2d5e80 ffff88904f2d5e80
>>> 0000000000000000
>>> [    0.123954] raw: 0000000000000000 0000000000000000 00000000ffffff7f
>>> 0000000000000000
>>> [    0.123955] page dumped because: nonzero mapcount
>>> [    0.123957] Modules linked in:
>>> [    0.123961] CPU: 0 PID: 0 Comm: swapper Not tainted
>>> 5.16.0-rc3-sos-custom #2
>>> [    0.123964] Hardware name: AMD Corporation
>>> [    0.123967] Call Trace:
>>> [    0.123971]  <TASK>
>>> [    0.123975]  dump_stack_lvl+0x48/0x5e
>>> [    0.123985]  bad_page.cold+0x65/0x96
>>> [    0.123990]  __free_pages_ok+0x3a8/0x410
>>> [    0.123996]  memblock_free_all+0x171/0x1dc
>>> [    0.124005]  mem_init+0x1f/0x14b
>>> [    0.124011]  start_kernel+0x3b5/0x6a1
>>> [    0.124016]  secondary_startup_64_no_verify+0xb0/0xbb
>>> [    0.124022]  </TASK>
>>>
>>> I see ~40 of these traces, each for different pfns.
>>>
>>> Thanks,
>>> Tom
>>
>> Hi Tom:
>>        Thanks for your test. Could you help to test the following patch
>> and check whether it can fix the issue.
>
> The patch is mangled. Is the only difference where set_memory_decrypted()
> is called?

I de-mangled the patch. No more stack traces with SME active.

Thanks,
Tom

>
> Thanks,
> Tom
>
>>
>>
>> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
>> index 569272871375..f6c3638255d5 100644
>> --- a/include/linux/swiotlb.h
>> +++ b/include/linux/swiotlb.h
>> @@ -73,6 +73,9 @@ extern enum swiotlb_force swiotlb_force;
>>    * @end:       The end address of the swiotlb memory pool. Used to do
>> a quick
>>    *             range check to see if the memory was in fact allocated
>> by this
>>    *             API.
>> + * @vaddr:     The vaddr of the swiotlb memory pool. The swiotlb memory
>> pool
>> + *             may be remapped in the memory encrypted case and store
>> virtual
>> + *             address for bounce buffer operation.
>>    * @nslabs:    The number of IO TLB blocks (in groups of 64) between
>> @start and
>>    *             @end. For default swiotlb, this is command line
>> adjustable via
>>    *             setup_io_tlb_npages.
>> @@ -92,6 +95,7 @@ extern enum swiotlb_force swiotlb_force;
>>   struct io_tlb_mem {
>>          phys_addr_t start;
>>          phys_addr_t end;
>> +       void *vaddr;
>>          unsigned long nslabs;
>>          unsigned long used;
>>          unsigned int index;
>> @@ -186,4 +190,6 @@ static inline bool is_swiotlb_for_alloc(struct
>> device *dev)
>>   }
>>   #endif /* CONFIG_DMA_RESTRICTED_POOL */
>>
>> +extern phys_addr_t swiotlb_unencrypted_base;
>> +
>>   #endif /* __LINUX_SWIOTLB_H */
>> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
>> index 8e840fbbed7c..34e6ade4f73c 100644
>> --- a/kernel/dma/swiotlb.c
>> +++ b/kernel/dma/swiotlb.c
>> @@ -50,6 +50,7 @@
>>   #include <asm/io.h>
>>   #include <asm/dma.h>
>>
>> +#include <linux/io.h>
>>   #include <linux/init.h>
>>   #include <linux/memblock.h>
>>   #include <linux/iommu-helper.h>
>> @@ -72,6 +73,8 @@ enum swiotlb_force swiotlb_force;
>>
>>   struct io_tlb_mem io_tlb_default_mem;
>>
>> +phys_addr_t swiotlb_unencrypted_base;
>> +
>>   /*
>>    * Max segment that we can provide which (if pages are contingous) will
>>    * not be bounced (unless SWIOTLB_FORCE is set).
>> @@ -155,6 +158,27 @@ static inline unsigned long nr_slots(u64 val)
>>          return DIV_ROUND_UP(val, IO_TLB_SIZE);
>>   }
>>
>> +/*
>> + * Remap swioltb memory in the unencrypted physical address space
>> + * when swiotlb_unencrypted_base is set. (e.g. for Hyper-V AMD SEV-SNP
>> + * Isolation VMs).
>> + */
>> +void *swiotlb_mem_remap(struct io_tlb_mem *mem, unsigned long bytes)
>> +{
>> +       void *vaddr = NULL;
>> +
>> +       if (swiotlb_unencrypted_base) {
>> +               phys_addr_t paddr = mem->start + swiotlb_unencrypted_base;
>> +
>> +               vaddr = memremap(paddr, bytes, MEMREMAP_WB);
>> +               if (!vaddr)
>> +                       pr_err("Failed to map the unencrypted memory
>> %llx size %lx.\n",
>> +                              paddr, bytes);
>> +       }
>> +
>> +       return vaddr;
>> +}
>> +
>>   /*
>>    * Early SWIOTLB allocation may be too early to allow an architecture to
>>    * perform the desired operations.  This function allows the
>> architecture to
>> @@ -172,7 +196,12 @@ void __init swiotlb_update_mem_attributes(void)
>>          vaddr = phys_to_virt(mem->start);
>>          bytes = PAGE_ALIGN(mem->nslabs << IO_TLB_SHIFT);
>>          set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);
>> -       memset(vaddr, 0, bytes);
>> +
>> +       mem->vaddr = swiotlb_mem_remap(mem, bytes);
>> +       if (!mem->vaddr)
>> +               mem->vaddr = vaddr;
>> +
>> +       memset(mem->vaddr, 0, bytes);
>>   }
>>
>>   static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem,
>> phys_addr_t start,
>> @@ -196,7 +225,17 @@ static void swiotlb_init_io_tlb_mem(struct
>> io_tlb_mem *mem, phys_addr_t start,
>>                  mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
>>                  mem->slots[i].alloc_size = 0;
>>          }
>> +
>> +       /*
>> +        * If swiotlb_unencrypted_base is set, the bounce buffer memory
>> will
>> +        * be remapped and cleared in swiotlb_update_mem_attributes.
>> +        */
>> +       if (swiotlb_unencrypted_base)
>> +               return;
>> +
>>          memset(vaddr, 0, bytes);
>> +       mem->vaddr = vaddr;
>> +       return;
>>   }
>>
>>   int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int
>> verbose)
>> @@ -371,7 +410,7 @@ static void swiotlb_bounce(struct device *dev,
>> phys_addr_t tlb_addr, size_t size
>>          phys_addr_t orig_addr = mem->slots[index].orig_addr;
>>          size_t alloc_size = mem->slots[index].alloc_size;
>>          unsigned long pfn = PFN_DOWN(orig_addr);
>> -       unsigned char *vaddr = phys_to_virt(tlb_addr);
>> +       unsigned char *vaddr = mem->vaddr + tlb_addr - mem->start;
>>          unsigned int tlb_offset, orig_addr_offset;
>>
>>          if (orig_addr == INVALID_PHYS_ADDR)
>>
>>
>> Thanks.
>>