On Wed, Apr 14, 2021 at 10:49:42AM -0400, Tianyu Lan wrote:
> From: Tianyu Lan <tianyu....@microsoft.com>
>
> For Hyper-V isolation VM with AMD SEV SNP, the bounce buffer(shared memory)
> needs to be accessed via extra address space(e.g address above bit39).
> Hyper-V code may remap extra address space outside of swiotlb.
> swiotlb_bounce()
May? Isn't this a MUST in this case?
> needs to use remap virtual address to copy data from/to bounce buffer. Add
> new interface swiotlb_set_bounce_remap() to do that.
I am bit lost - why can't you use the swiotlb_init and pass in your
DMA pool that is already above bit 39?
>
> Signed-off-by: Tianyu Lan <tianyu....@microsoft.com>
> ---
> include/linux/swiotlb.h | 5 +++++
> kernel/dma/swiotlb.c | 13 ++++++++++++-
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index d9c9fc9ca5d2..3ccd08116683 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -82,8 +82,13 @@ unsigned int swiotlb_max_segment(void);
> size_t swiotlb_max_mapping_size(struct device *dev);
> bool is_swiotlb_active(void);
> void __init swiotlb_adjust_size(unsigned long new_size);
> +void swiotlb_set_bounce_remap(unsigned char *vaddr);
> #else
> #define swiotlb_force SWIOTLB_NO_FORCE
> +static inline void swiotlb_set_bounce_remap(unsigned char *vaddr)
> +{
> +}
> +
> static inline bool is_swiotlb_buffer(phys_addr_t paddr)
> {
> return false;
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 7c42df6e6100..5fd2db6aa149 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -94,6 +94,7 @@ static unsigned int io_tlb_index;
> * not be bounced (unless SWIOTLB_FORCE is set).
> */
> static unsigned int max_segment;
> +static unsigned char *swiotlb_bounce_remap_addr;
>
> /*
> * We need to save away the original address corresponding to a mapped entry
> @@ -421,6 +422,11 @@ void __init swiotlb_exit(void)
> swiotlb_cleanup();
> }
>
> +void swiotlb_set_bounce_remap(unsigned char *vaddr)
> +{
> + swiotlb_bounce_remap_addr = vaddr;
> +}
> +
> /*
> * Bounce: copy the swiotlb buffer from or back to the original dma location
> */
> @@ -428,7 +434,12 @@ static void swiotlb_bounce(phys_addr_t orig_addr,
> phys_addr_t tlb_addr,
> size_t size, enum dma_data_direction dir)
> {
> unsigned long pfn = PFN_DOWN(orig_addr);
> - unsigned char *vaddr = phys_to_virt(tlb_addr);
> + unsigned char *vaddr;
> +
> + if (swiotlb_bounce_remap_addr)
> + vaddr = swiotlb_bounce_remap_addr + tlb_addr - io_tlb_start;
> + else
> + vaddr = phys_to_virt(tlb_addr);
>
> if (PageHighMem(pfn_to_page(pfn))) {
> /* The buffer does not have a mapping. Map it in and copy */
> --
> 2.25.1
>
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