NAK: [PATCH] UBUNTU: SAUCE: azure: Swiotlb: Add swiotlb_alloc_from_low_pages switch

[Tim Gardner]

Missing proper subject. v2 on the way.

On 3/30/22 11:48, Tim Gardner wrote:
> From: Tianyu Lan <Tianyu.Lan at microsoft.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1967166
> 
> Hyper-V Isolation VM and AMD SEV VM uses swiotlb bounce buffer to
> share memory with hypervisor. Current swiotlb bounce buffer is only
> allocated from 0 to ARCH_LOW_ADDRESS_LIMIT which is default to
> 0xffffffffUL. Isolation VM and AMD SEV VM needs 1G bounce buffer at most.
> This will fail when there is not enough memory from 0 to 4G address
> space and devices also may use memory above 4G address space as DMA memory.
> Expose swiotlb_alloc_from_low_pages and platform mey set it to false when
> it's not necessary to limit bounce buffer from 0 to 4G memory.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan at microsoft.com>
> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
> ---
> 
> This patch depends on a previous pull request:
> [Pull Request] [impish/linux-azure] Azure: Update Hyperv to 5.17
> 
> ---
>   include/linux/swiotlb.h |  1 +
>   kernel/dma/swiotlb.c    | 17 +++++++++++++++--
>   2 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 2356da25c3b9..037356d57abf 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -38,6 +38,7 @@ enum swiotlb_force {
>   extern void swiotlb_init(int verbose);
>   int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
>   unsigned long swiotlb_size_or_default(void);
> +void swiotlb_set_alloc_from_low_pages(bool low);
>   extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
>   extern int swiotlb_late_init_with_default_size(size_t default_size);
>   extern void __init swiotlb_update_mem_attributes(void);
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index c57e78071143..e2c1395740de 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -67,6 +67,7 @@ enum swiotlb_force swiotlb_force;
>   struct io_tlb_mem *io_tlb_default_mem;
>   
>   phys_addr_t swiotlb_unencrypted_base;
> +static bool swiotlb_alloc_from_low_pages = true;
>   
>   /*
>    * Max segment that we can provide which (if pages are contingous) will
> @@ -109,6 +110,11 @@ void swiotlb_set_max_segment(unsigned int val)
>   		max_segment = rounddown(val, PAGE_SIZE);
>   }
>   
> +void swiotlb_set_alloc_from_low_pages(bool low)
> +{
> +	swiotlb_alloc_from_low_pages = low;
> +}
> +
>   unsigned long swiotlb_size_or_default(void)
>   {
>   	return default_nslabs << IO_TLB_SHIFT;
> @@ -253,8 +259,15 @@ swiotlb_init(int verbose)
>   	if (swiotlb_force == SWIOTLB_NO_FORCE)
>   		return;
>   
> -	/* Get IO TLB memory from the low pages */
> -	tlb = memblock_alloc_low(bytes, PAGE_SIZE);
> +	/*
> +	 * Get IO TLB memory from the low pages if swiotlb_alloc_from_low_pages
> +	 * is set.
> +	 */
> +	if (swiotlb_alloc_from_low_pages)
> +		tlb = memblock_alloc_low(bytes, PAGE_SIZE);
> +	else
> +		tlb = memblock_alloc(bytes, PAGE_SIZE);
> +
>   	if (!tlb)
>   		goto fail;
>   	if (swiotlb_init_with_tbl(tlb, default_nslabs, verbose))

-- 
-----------
Tim Gardner
Canonical, Inc