linux-kernel - [PATCH v2] RISC-V: KVM: Remove automatic I/O mapping for VM

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Message-Id: <20251021142131.78796-1-fangyu.yu@linux.alibaba.com>
Date: Tue, 21 Oct 2025 22:21:31 +0800
From: fangyu.yu@...ux.alibaba.com
To: anup@...infault.org,
	atish.patra@...ux.dev,
	pjw@...nel.org,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	pbonzini@...hat.com,
	jiangyifei@...wei.com
Cc: guoren@...nel.org,
	dbarboza@...tanamicro.com,
	kvm@...r.kernel.org,
	kvm-riscv@...ts.infradead.org,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Fangyu Yu <fangyu.yu@...ux.alibaba.com>
Subject: [PATCH v2] RISC-V: KVM: Remove automatic I/O mapping for VM_PFNMAP

From: Fangyu Yu <fangyu.yu@...ux.alibaba.com>

As of commit aac6db75a9fc ("vfio/pci: Use unmap_mapping_range()"),
vm_pgoff may no longer guaranteed to hold the PFN for VM_PFNMAP
regions. Using vma->vm_pgoff to derive the HPA here may therefore
produce incorrect mappings.

Instead, I/O mappings for such regions can be established on-demand
during g-stage page faults, making the upfront ioremap in this path
is unnecessary.

Fixes: 9d05c1fee837 ("RISC-V: KVM: Implement stage2 page table programming")
Signed-off-by: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
Tested-by: Daniel Henrique Barboza <dbarboza@...tanamicro.com>

---
Changes in v2:
- Fixed build warnings.
---
 arch/riscv/kvm/mmu.c | 25 ++-----------------------
 1 file changed, 2 insertions(+), 23 deletions(-)

diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index 525fb5a330c0..58f5f3536ffd 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -171,7 +171,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				enum kvm_mr_change change)
 {
 	hva_t hva, reg_end, size;
-	gpa_t base_gpa;
 	bool writable;
 	int ret = 0;
 
@@ -190,15 +189,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	hva = new->userspace_addr;
 	size = new->npages << PAGE_SHIFT;
 	reg_end = hva + size;
-	base_gpa = new->base_gfn << PAGE_SHIFT;
 	writable = !(new->flags & KVM_MEM_READONLY);
 
 	mmap_read_lock(current->mm);
 
 	/*
 	 * A memory region could potentially cover multiple VMAs, and
-	 * any holes between them, so iterate over all of them to find
-	 * out if we can map any of them right now.
+	 * any holes between them, so iterate over all of them.
 	 *
 	 *     +--------------------------------------------+
 	 * +---------------+----------------+   +----------------+
@@ -209,7 +206,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	 */
 	do {
 		struct vm_area_struct *vma;
-		hva_t vm_start, vm_end;
+		hva_t vm_end;
 
 		vma = find_vma_intersection(current->mm, hva, reg_end);
 		if (!vma)
@@ -225,36 +222,18 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 		}
 
 		/* Take the intersection of this VMA with the memory region */
-		vm_start = max(hva, vma->vm_start);
 		vm_end = min(reg_end, vma->vm_end);
 
 		if (vma->vm_flags & VM_PFNMAP) {
-			gpa_t gpa = base_gpa + (vm_start - hva);
-			phys_addr_t pa;
-
-			pa = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
-			pa += vm_start - vma->vm_start;
-
 			/* IO region dirty page logging not allowed */
 			if (new->flags & KVM_MEM_LOG_DIRTY_PAGES) {
 				ret = -EINVAL;
 				goto out;
 			}
-
-			ret = kvm_riscv_mmu_ioremap(kvm, gpa, pa, vm_end - vm_start,
-						    writable, false);
-			if (ret)
-				break;
 		}
 		hva = vm_end;
 	} while (hva < reg_end);
 
-	if (change == KVM_MR_FLAGS_ONLY)
-		goto out;
-
-	if (ret)
-		kvm_riscv_mmu_iounmap(kvm, base_gpa, size);
-
 out:
 	mmap_read_unlock(current->mm);
 	return ret;
-- 
2.50.1