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

Tianyu Lan
2021-12-03T11:20:22Z

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.

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.