linux-kernel - [RFC PATCH v2 1/2] kvm/arm64: Remove the creation time's mapping of MMIO regions

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Date:   Tue, 16 Mar 2021 21:43:37 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <kvm@...r.kernel.org>,
        <kvmarm@...ts.cs.columbia.edu>, Will Deacon <will@...nel.org>,
        Marc Zyngier <maz@...nel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        <wanghaibin.wang@...wei.com>, <jiangkunkun@...wei.com>,
        <yuzenghui@...wei.com>, <lushenming@...wei.com>
Subject: [RFC PATCH v2 1/2] kvm/arm64: Remove the creation time's mapping of MMIO regions

The MMIO regions may be unmapped for many reasons and can be remapped
by stage2 fault path. Map MMIO regions at creation time becomes a
minor optimization and makes these two mapping path hard to sync.

Remove the mapping code while keep the useful sanity check.

Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
---
 arch/arm64/kvm/mmu.c | 38 +++-----------------------------------
 1 file changed, 3 insertions(+), 35 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 8711894db8c2..c59af5ca01b0 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1301,7 +1301,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 {
 	hva_t hva = mem->userspace_addr;
 	hva_t reg_end = hva + mem->memory_size;
-	bool writable = !(mem->flags & KVM_MEM_READONLY);
 	int ret = 0;
 
 	if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
@@ -1318,8 +1317,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	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.
+	 * between them, so iterate over all of them.
 	 *
 	 *     +--------------------------------------------+
 	 * +---------------+----------------+   +----------------+
@@ -1330,50 +1328,20 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	 */
 	do {
 		struct vm_area_struct *vma = find_vma(current->mm, hva);
-		hva_t vm_start, vm_end;
 
 		if (!vma || vma->vm_start >= reg_end)
 			break;
 
-		/*
-		 * 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 = mem->guest_phys_addr +
-				    (vm_start - mem->userspace_addr);
-			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 (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES) {
 				ret = -EINVAL;
-				goto out;
-			}
-
-			ret = kvm_phys_addr_ioremap(kvm, gpa, pa,
-						    vm_end - vm_start,
-						    writable);
-			if (ret)
 				break;
+			}
 		}
-		hva = vm_end;
+		hva = min(reg_end, vma->vm_end);
 	} while (hva < reg_end);
 
-	if (change == KVM_MR_FLAGS_ONLY)
-		goto out;
-
-	spin_lock(&kvm->mmu_lock);
-	if (ret)
-		unmap_stage2_range(&kvm->arch.mmu, mem->guest_phys_addr, mem->memory_size);
-	else if (!cpus_have_final_cap(ARM64_HAS_STAGE2_FWB))
-		stage2_flush_memslot(kvm, memslot);
-	spin_unlock(&kvm->mmu_lock);
-out:
 	mmap_read_unlock(current->mm);
 	return ret;
 }
-- 
2.19.1