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Tue, 28 Oct 2025 04:44:07 -0700 (PDT) Message-ID: Date: Tue, 28 Oct 2025 11:44:06 +0000 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/4] KVM: selftests: Fix unaligned mmap allocations Content-Language: en-GB To: Sean Christopherson Cc: maz@kernel.org, oliver.upton@linux.dev, pbonzini@redhat.com, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, shuah@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, isaku.yamahata@intel.com, roypat@amazon.co.uk, kalyazin@amazon.co.uk, jackabt@amazon.com References: <20251013151502.6679-1-jackabt.amazon@gmail.com> <20251013151502.6679-3-jackabt.amazon@gmail.com> From: "Thomson, Jack" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 23/10/2025 6:16 pm, Sean Christopherson wrote: > On Mon, Oct 13, 2025, Jack Thomson wrote: >> From: Jack Thomson >> >> 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. > > What happens when selftests use the wrong map_size? E.g. is munmap() silently > failing? If so, then I should probably take this particular patch through > kvm-x86/gmem, otherwise it means we'll start getting asserts due to: > > 3223560c93eb ("KVM: selftests: Define wrappers for common syscalls to assert success") > > If munmap() isn't failing, then that begs the question of what this patch is > actually doing :-) > Hi Sean, sorry I completely missed your reply. Yeah currently with a misaligned map_size it causes munmap() to fail, I noticed when tested with different backings. >> Update the vm_mem_add method to ensure the mmap_size is aligned to the >> underlying page size. >> >> Signed-off-by: Jack Thomson >> --- >> 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 >> -- Thanks, Jack