RE: [PATCH V5 09/12] x86/Swiotlb: Add Swiotlb bounce buffer remap function for HV IVM

Michael Kelley
2021-09-15T15:42:44Z

From: Tianyu Lan <ltykernel@gmail.com> Sent: Tuesday, September 14, 2021 6:39 AM
>
> 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 call memremap() to map bounce buffer in the
> swiotlb code, store map address and use the address to copy data
> from/to swiotlb bounce buffer.
>
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
> ---
> Change since v4:
> * Expose swiotlb_unencrypted_base to set unencrypted memory
> offset.
> * Use memremap() to map bounce buffer if swiotlb_unencrypted_
> base is set.
>
> Change since v1:
> * Make swiotlb_init_io_tlb_mem() return error code and return
> error when dma_map_decrypted() fails.
> ---
> include/linux/swiotlb.h | 6 ++++++
> kernel/dma/swiotlb.c | 41 +++++++++++++++++++++++++++++++++++------
> 2 files changed, 41 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index b0cb2a9973f4..4998ed44ae3d 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -72,6 +72,9 @@ 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.
> @@ -91,6 +94,7 @@ 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;
> @@ -185,4 +189,6 @@ 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 87c40517e822..9e30cc4bd872 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).
> @@ -175,7 +178,7 @@ void __init swiotlb_update_mem_attributes(void)
> memset(vaddr, 0, bytes);
> }
>
> -static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
> +static int swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
> unsigned long nslabs, bool late_alloc)
> {
> void *vaddr = phys_to_virt(start);
> @@ -196,13 +199,34 @@ 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 (set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT))
> + return -EFAULT;
> +
> + /*
> + * Map memory in the unencrypted physical address space when requested
> + * (e.g. for Hyper-V AMD SEV-SNP Isolation VMs).
> + */
> + if (swiotlb_unencrypted_base) {
> + phys_addr_t paddr = __pa(vaddr) + swiotlb_unencrypted_base;

Nit: Use "start" instead of "__pa(vaddr)" since "start" is already the needed
physical address.

> +
> + vaddr = memremap(paddr, bytes, MEMREMAP_WB);
> + if (!vaddr) {
> + pr_err("Failed to map the unencrypted memory.\n");
> + return -ENOMEM;
> + }
> + }
> +
> memset(vaddr, 0, bytes);
> + mem->vaddr = vaddr;
> + return 0;
> }
>
> int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> {
> struct io_tlb_mem *mem = &io_tlb_default_mem;
> size_t alloc_size;
> + int ret;
>
> if (swiotlb_force == SWIOTLB_NO_FORCE)
> return 0;
> @@ -217,7 +241,11 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> panic("%s: Failed to allocate %zu bytes align=0x%lx\n",
> __func__, alloc_size, PAGE_SIZE);
>
> - swiotlb_init_io_tlb_mem(mem, __pa(tlb), nslabs, false);
> + ret = swiotlb_init_io_tlb_mem(mem, __pa(tlb), nslabs, false);
> + if (ret) {
> + memblock_free(__pa(mem), alloc_size);
> + return ret;
> + }
>
> if (verbose)
> swiotlb_print_info();
> @@ -304,7 +332,7 @@ int
> swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
> {
> struct io_tlb_mem *mem = &io_tlb_default_mem;
> - unsigned long bytes = nslabs << IO_TLB_SHIFT;
> + int ret;
>
> if (swiotlb_force == SWIOTLB_NO_FORCE)
> return 0;
> @@ -318,8 +346,9 @@ 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);
> + ret = swiotlb_init_io_tlb_mem(mem, virt_to_phys(tlb), nslabs, true);
> + if (ret)

Before returning the error, free the pages obtained from the earlier call
to __get_free_pages()?

> + return ret;
>
> swiotlb_print_info();
> swiotlb_set_max_segment(mem->nslabs << IO_TLB_SHIFT);
> @@ -371,7 +400,7 @@ 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)
> --
> 2.25.1