linux-kernel - [PATCH 4/6] KVM: selftests: Fix unaligned mmap allocations

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Message-Id: <20250911134648.58945-5-jackabt.amazon@gmail.com>
Date: Thu, 11 Sep 2025 14:46:46 +0100
From: Jack Thomson <jackabt.amazon@...il.com>
To: maz@...nel.org,
	oliver.upton@...ux.dev,
	pbonzini@...hat.com
Cc: joey.gouly@....com,
	suzuki.poulose@....com,
	yuzenghui@...wei.com,
	catalin.marinas@....com,
	will@...nel.org,
	shuah@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	isaku.yamahata@...el.com,
	roypat@...zon.co.uk,
	kalyazin@...zon.co.uk,
	jackabt@...zon.com
Subject: [PATCH 4/6] KVM: selftests: Fix unaligned mmap allocations

From: Jack Thomson <jackabt@...zon.com>

When creating a VM using mmap with huge pages, and the memory amount does
not align with the underlying page size. The stored mmap_size value does
not account for the fact that mmap will automatically align the length
to a multiple of the underlying page size. During the teardown of the
test, munmap is used. However, munmap requires the length to be a
multiple of the underlying page size.

Update the vm_mem_add method to ensure the mmap_size is aligned to the
underlying page size.

Signed-off-by: Jack Thomson <jackabt@...zon.com>
---
 tools/testing/selftests/kvm/lib/kvm_util.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index c3f5142b0a54..b106fbed999c 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1051,7 +1051,6 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 	/* Allocate and initialize new mem region structure. */
 	region = calloc(1, sizeof(*region));
 	TEST_ASSERT(region != NULL, "Insufficient Memory");
-	region->mmap_size = mem_size;
 
 #ifdef __s390x__
 	/* On s390x, the host address must be aligned to 1M (due to PGSTEs) */
@@ -1060,6 +1059,11 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 	alignment = 1;
 #endif
 
+	alignment = max(backing_src_pagesz, alignment);
+	region->mmap_size = align_up(mem_size, alignment);
+
+	TEST_ASSERT_EQ(guest_paddr, align_up(guest_paddr, backing_src_pagesz));
+
 	/*
 	 * When using THP mmap is not guaranteed to returned a hugepage aligned
 	 * address so we have to pad the mmap. Padding is not needed for HugeTLB
@@ -1067,12 +1071,6 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type,
 	 * page size.
 	 */
 	if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
-		alignment = max(backing_src_pagesz, alignment);
-
-	TEST_ASSERT_EQ(guest_paddr, align_up(guest_paddr, backing_src_pagesz));
-
-	/* Add enough memory to align up if necessary */
-	if (alignment > 1)
 		region->mmap_size += alignment;
 
 	region->fd = -1;
-- 
2.43.0