linux-kernel - Re: [PATCH] KVM: selftests: Fix mapping length truncation in m{,un}map()

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Date:   Wed, 30 Jun 2021 09:37:54 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Zenghui Yu <yuzenghui@...wei.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com
Cc:     wanghaibin.wang@...wei.com
Subject: Re: [PATCH] KVM: selftests: Fix mapping length truncation in
 m{,un}map()



On 24.06.21 09:09, Zenghui Yu wrote:
> max_mem_slots is now declared as uint32_t. The result of (0x200000 * 32767)
> is unexpectedly truncated to be 0xffe00000, whilst we actually need to
> allocate about, 63GB. Cast max_mem_slots to size_t in both mmap() and
> munmap() to fix the length truncation.
> 
> We'll otherwise see the failure on arm64 thanks to the access_ok() checking
> in __kvm_set_memory_region(), as the unmapped VA happen to go beyond the
> task's allowed address space.
> 
>   # ./set_memory_region_test
> Allowed number of memory slots: 32767
> Adding slots 0..32766, each memory region with 2048K size
> ==== Test Assertion Failure ====
>    set_memory_region_test.c:391: ret == 0
>    pid=94861 tid=94861 errno=22 - Invalid argument
>       1	0x00000000004015a7: test_add_max_memory_regions at set_memory_region_test.c:389
>       2	 (inlined by) main at set_memory_region_test.c:426
>       3	0x0000ffffb8e67bdf: ?? ??:0
>       4	0x00000000004016db: _start at :?
>    KVM_SET_USER_MEMORY_REGION IOCTL failed,
>    rc: -1 errno: 22 slot: 2615
> 
> Fixes: 3bf0fcd75434 ("KVM: selftests: Speed up set_memory_region_test")
> Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>

While likely correct, this now breaks on many test systems in our CI that have less memory than 64GB.
(We do get ENOMEM). I have not seen the ENOMEM failures in earlier versions. Strange

> ---
>   tools/testing/selftests/kvm/set_memory_region_test.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
> index d79d58eada9f..85b18bb8f762 100644
> --- a/tools/testing/selftests/kvm/set_memory_region_test.c
> +++ b/tools/testing/selftests/kvm/set_memory_region_test.c
> @@ -376,7 +376,7 @@ static void test_add_max_memory_regions(void)
>   	pr_info("Adding slots 0..%i, each memory region with %dK size\n",
>   		(max_mem_slots - 1), MEM_REGION_SIZE >> 10);
> 
> -	mem = mmap(NULL, MEM_REGION_SIZE * max_mem_slots + alignment,
> +	mem = mmap(NULL, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment,
>   		   PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>   	TEST_ASSERT(mem != MAP_FAILED, "Failed to mmap() host");
>   	mem_aligned = (void *)(((size_t) mem + alignment - 1) & ~(alignment - 1));
> @@ -401,7 +401,7 @@ static void test_add_max_memory_regions(void)
>   	TEST_ASSERT(ret == -1 && errno == EINVAL,
>   		    "Adding one more memory slot should fail with EINVAL");
> 
> -	munmap(mem, MEM_REGION_SIZE * max_mem_slots + alignment);
> +	munmap(mem, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment);
>   	munmap(mem_extra, MEM_REGION_SIZE);
>   	kvm_vm_free(vm);
>   }
>