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

Tom Lendacky
2021-12-02T14:42:55Z

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

> ---
> Change since v2:
> * Leave mem->vaddr with phys_to_virt(mem->start) when fail
> to remap swiotlb memory.
>
> Change since v1:
> * Rework comment in the swiotlb_init_io_tlb_mem()
> * Make swiotlb_init_io_tlb_mem() back to return void.
> ---
> include/linux/swiotlb.h | 6 ++++++
> kernel/dma/swiotlb.c | 47 ++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 48 insertions(+), 5 deletions(-)
>
> 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..adb9d06af5c8 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 +225,18 @@ 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;
> +
> + set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);
> memset(vaddr, 0, bytes);
> + mem->vaddr = vaddr;
> + return;
> }
>
> int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> @@ -318,7 +358,6 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
> if (!mem->slots)
> return -ENOMEM;
>
> - set_memory_decrypted((unsigned long)tlb, bytes >> PAGE_SHIFT);
> swiotlb_init_io_tlb_mem(mem, virt_to_phys(tlb), nslabs, true);
>
> swiotlb_print_info();
> @@ -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)
> @@ -806,8 +845,6 @@ static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
> return -ENOMEM;
> }
>
> - set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
> - rmem->size >> PAGE_SHIFT);
> swiotlb_init_io_tlb_mem(mem, rmem->base, nslabs, false);
> mem->force_bounce = true;
> mem->for_alloc = true;
>