Re: [PATCH] arm64: swiotlb: Keep the default size for protected guests
From: Will Deacon <will@kernel.org>
Date: 2026-08-07 11:58:47
Also in:
linux-arm-kernel, linux-coco, linux-iommu, linux-s390, lkml
On Fri, Aug 07, 2026 at 02:56:12PM +0530, Aneesh Kumar K.V (Arm) wrote:
quoted hunk ↗ jump to hunk
Realm guests and protected KVM guests may require swiotlb for device DMA even when all system RAM is addressable by the DMA zones. Do not reduce the SWIOTLB buffer to the kmalloc-bouncing size for these guests, as the reduced number of slots can be exhausted during CCA guest operation. Fixes: 30c5e45ee2c5 ("dma-direct: make dma_direct_map_phys() honor DMA_ATTR_CC_SHARED") Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org> --- arch/arm64/mm/init.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index e308a7cabd12..24caaf10e755 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c@@ -339,7 +339,8 @@ void __init arch_mm_preinit(void) { unsigned int flags = SWIOTLB_VERBOSE; - if (max_pfn <= PFN_DOWN(arm64_dma_phys_limit)) { + if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) && + max_pfn <= PFN_DOWN(arm64_dma_phys_limit)) {
Protected guests under pKVM rely on restricted DMA, so won't this just waste memory for them? Will