linux-kernel - [PATCH v4 12/28] KVM: arm64: iommu: Support DABT for IOMMU

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Message-ID: <20250819215156.2494305-13-smostafa@google.com>
Date: Tue, 19 Aug 2025 21:51:40 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev
Cc: maz@...nel.org, oliver.upton@...ux.dev, joey.gouly@....com, 
	suzuki.poulose@....com, yuzenghui@...wei.com, catalin.marinas@....com, 
	will@...nel.org, robin.murphy@....com, jean-philippe@...aro.org, 
	qperret@...gle.com, tabba@...gle.com, jgg@...pe.ca, mark.rutland@....com, 
	praan@...gle.com, Mostafa Saleh <smostafa@...gle.com>
Subject: [PATCH v4 12/28] KVM: arm64: iommu: Support DABT for IOMMU

SMMUv3 driver need to trap and emulate access to the MMIO space as
part of the nested implementation.

Add a handler for DABTs for IOMMU drivers to be able to do so, in
case the host fault in page, check if it's part of IOMMU emulation
first.

Signed-off-by: Mostafa Saleh <smostafa@...gle.com>
---
 arch/arm64/include/asm/kvm_arm.h        |  2 ++
 arch/arm64/kvm/hyp/include/nvhe/iommu.h |  3 ++-
 arch/arm64/kvm/hyp/nvhe/iommu/iommu.c   | 15 +++++++++++++++
 arch/arm64/kvm/hyp/nvhe/mem_protect.c   | 10 ++++++++++
 4 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
index 1da290aeedce..8d63308ccd5c 100644
--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -331,6 +331,8 @@
 
 /* Hyp Prefetch Fault Address Register (HPFAR/HDFAR) */
 #define HPFAR_MASK	(~UL(0xf))
+
+#define FAR_MASK GENMASK_ULL(11, 0)
 /*
  * We have
  *	PAR	[PA_Shift - 1	: 12] = PA	[PA_Shift - 1 : 12]
diff --git a/arch/arm64/kvm/hyp/include/nvhe/iommu.h b/arch/arm64/kvm/hyp/include/nvhe/iommu.h
index 9f4906c6dcc9..10fe4fbf7424 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/iommu.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/iommu.h
@@ -8,6 +8,7 @@
 struct kvm_iommu_ops {
 	int (*init)(void);
 	void (*host_stage2_idmap)(phys_addr_t start, phys_addr_t end, int prot);
+	bool (*dabt_handler)(struct user_pt_regs *regs, u64 esr, u64 addr);
 };
 
 int kvm_iommu_init(void *pool_base, size_t nr_pages);
@@ -16,5 +17,5 @@ void kvm_iommu_host_stage2_idmap(phys_addr_t start, phys_addr_t end,
 				 enum kvm_pgtable_prot prot);
 void *kvm_iommu_donate_pages(u8 order);
 void kvm_iommu_reclaim_pages(void *ptr);
-
+bool kvm_iommu_host_dabt_handler(struct user_pt_regs *regs, u64 esr, u64 addr);
 #endif /* __ARM64_KVM_NVHE_IOMMU_H__ */
diff --git a/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c b/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
index 1673165c7330..376b30f557a2 100644
--- a/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
+++ b/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
@@ -4,6 +4,10 @@
  *
  * Copyright (C) 2022 Linaro Ltd.
  */
+#include <asm/kvm_hyp.h>
+
+#include <hyp/adjust_pc.h>
+
 #include <linux/iommu.h>
 
 #include <nvhe/iommu.h>
@@ -113,3 +117,14 @@ void kvm_iommu_reclaim_pages(void *ptr)
 {
 	hyp_put_page(&iommu_pages_pool, ptr);
 }
+
+bool kvm_iommu_host_dabt_handler(struct user_pt_regs *regs, u64 esr, u64 addr)
+{
+	if (kvm_iommu_ops && kvm_iommu_ops->dabt_handler &&
+	    kvm_iommu_ops->dabt_handler(regs, esr, addr)) {
+		/* DABT handled by the driver, skip to next instruction. */
+		kvm_skip_host_instr();
+		return true;
+	}
+	return false;
+}
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index bce6690f29c0..7371b2183e1e 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -595,6 +595,11 @@ static int host_stage2_idmap(u64 addr)
 	return ret;
 }
 
+static bool is_dabt(u64 esr)
+{
+	return ESR_ELx_EC(esr) == ESR_ELx_EC_DABT_LOW;
+}
+
 void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
 {
 	struct kvm_vcpu_fault_info fault;
@@ -617,6 +622,11 @@ void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
 	 */
 	BUG_ON(!(fault.hpfar_el2 & HPFAR_EL2_NS));
 	addr = FIELD_GET(HPFAR_EL2_FIPA, fault.hpfar_el2) << 12;
+	addr |= fault.far_el2 & FAR_MASK;
+
+	if (is_dabt(esr) && !addr_is_memory(addr) &&
+	    kvm_iommu_host_dabt_handler(&host_ctxt->regs, esr, addr))
+		return;
 
 	ret = host_stage2_idmap(addr);
 	BUG_ON(ret && ret != -EAGAIN);
-- 
2.51.0.rc1.167.g924127e9c0-goog