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Thu, 23 Oct 2025 10:16:06 -0700 (PDT) Date: Thu, 23 Oct 2025 10:16:05 -0700 In-Reply-To: <20251013151502.6679-3-jackabt.amazon@gmail.com> Mime-Version: 1.0 References: <20251013151502.6679-1-jackabt.amazon@gmail.com> <20251013151502.6679-3-jackabt.amazon@gmail.com> Message-ID: Subject: Re: [PATCH v2 2/4] KVM: selftests: Fix unaligned mmap allocations From: Sean Christopherson To: Jack Thomson 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 Content-Type: text/plain; charset="us-ascii" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251023_172043_513416_BD702DE7 X-CRM114-Status: GOOD ( 22.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 :-) > 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 >