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

Tom Lendacky
2021-12-03T19:11:27Z

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?

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.
>