linux-kernel - [RFC V1 4/5] x86: CVMs: Allow allocating all DMA memory from SWIOTLB

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Message-ID: <20240112055251.36101-5-vannapurve@google.com>
Date: Fri, 12 Jan 2024 05:52:50 +0000
From: Vishal Annapurve <vannapurve@...gle.com>
To: x86@...nel.org, linux-kernel@...r.kernel.org
Cc: pbonzini@...hat.com, rientjes@...gle.com, bgardon@...gle.com, 
	seanjc@...gle.com, erdemaktas@...gle.com, ackerleytng@...gle.com, 
	jxgao@...gle.com, sagis@...gle.com, oupton@...gle.com, peterx@...hat.com, 
	vkuznets@...hat.com, dmatlack@...gle.com, pgonda@...gle.com, 
	michael.roth@....com, kirill@...temov.name, thomas.lendacky@....com, 
	dave.hansen@...ux.intel.com, linux-coco@...ts.linux.dev, 
	chao.p.peng@...ux.intel.com, isaku.yamahata@...il.com, andrew.jones@...ux.dev, 
	corbet@....net, hch@....de, m.szyprowski@...sung.com, bp@...e.de, 
	rostedt@...dmis.org, iommu@...ts.linux.dev, 
	Vishal Annapurve <vannapurve@...gle.com>
Subject: [RFC V1 4/5] x86: CVMs: Allow allocating all DMA memory from SWIOTLB

Changes include:
1) Allocate all DMA memory from SWIOTLB buffers.
2) Increase the size of SWIOTLB region to accommodate dma_alloc_*
   invocations.
3) Align SWIOLTB regions to 2M size.

Signed-off-by: Vishal Annapurve <vannapurve@...gle.com>
---
 arch/x86/kernel/pci-dma.c | 2 +-
 arch/x86/mm/mem_encrypt.c | 8 ++++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index f323d83e40a7..3dcc3104b2a8 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -61,7 +61,7 @@ static void __init pci_swiotlb_detect(void)
 	 */
 	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
 		x86_swiotlb_enable = true;
-		x86_swiotlb_flags |= SWIOTLB_FORCE;
+		x86_swiotlb_flags |= (SWIOTLB_FORCE | SWIOTLB_ALLOC);
 	}
 }
 #else
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index c290c55b632b..0cf3365b051f 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -112,10 +112,14 @@ void __init mem_encrypt_setup_arch(void)
 	 * The percentage of guest memory used here for SWIOTLB buffers
 	 * is more of an approximation of the static adjustment which
 	 * 64MB for <1G, and ~128M to 256M for 1G-to-4G, i.e., the 6%
+	 *
+	 * Extra 2% is added to accommodate the requirement of DMA allocations
+	 * done using dma_alloc_* APIs.
 	 */
-	size = total_mem * 6 / 100;
-	size = clamp_val(size, IO_TLB_DEFAULT_SIZE, SZ_1G);
+	size = total_mem * 8 / 100;
+	size = clamp_val(size, IO_TLB_DEFAULT_SIZE, (SZ_1G + SZ_256M));
 	swiotlb_adjust_size(size);
+	swiotlb_adjust_alignment(SZ_2M);
 
 	/* Set restricted memory access for virtio. */
 	virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
-- 
2.43.0.275.g3460e3d667-goog