From: Tianyu Lan <ltykernel@xxxxxxxxx> Sent: Wednesday, January 26, 2022 8:11 AM > > 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 contiguous 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@xxxxxxxxxxxxx> > --- > include/linux/swiotlb.h | 1 + > kernel/dma/swiotlb.c | 13 +++++++++++-- > 2 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h > index f6c3638255d5..55c178e8eee0 100644 > --- a/include/linux/swiotlb.h > +++ b/include/linux/swiotlb.h > @@ -191,5 +191,6 @@ static inline bool is_swiotlb_for_alloc(struct device *dev) > #endif /* CONFIG_DMA_RESTRICTED_POOL */ > > extern phys_addr_t swiotlb_unencrypted_base; > +extern bool swiotlb_alloc_from_low_pages; > > #endif /* __LINUX_SWIOTLB_H */ > diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c > index f1e7ea160b43..159fef80f3db 100644 > --- a/kernel/dma/swiotlb.c > +++ b/kernel/dma/swiotlb.c > @@ -73,6 +73,12 @@ enum swiotlb_force swiotlb_force; > > struct io_tlb_mem io_tlb_default_mem; > > +/* > + * Get IO TLB memory from the low pages if swiotlb_alloc_from_low_pages > + * is set. > + */ > +bool swiotlb_alloc_from_low_pages = true; > + > phys_addr_t swiotlb_unencrypted_base; > > /* > @@ -284,8 +290,11 @@ 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); > + 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)) > -- > 2.25.1 Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
