The lam test does not set a guest memory size in x86/unittests.cfg, so QEMU falls back to the default of 128 MiB. AREA_NORMAL starts at PFN BIT(36-12), i.e. physical 64 GiB, which is never initialized in a 128 MiB guest. As a result, alloc_pages_flags(0, AREA_NORMAL) returns NULL and test_lam_user() ends up running its LAM checks against a NULL pointer, which is semantically meaningless even if the metadata-bit arithmetic happens to succeed. Allocate from AREA_LOW instead. AREA_LOW_PFN is BIT(24-12) (16 MiB), well within a 128 MiB guest, and bits 63..47 of the resulting linear address are still zero, so the LAM48/LAM57 metadata-bit checks remain valid. Update the adjacent comment accordingly. Fixes: 0164d7595c85 ("x86: Add test cases for LAM_{U48,U57}") Signed-off-by: Yexuan Yang --- v4: Change author information. v3: Change static_assert to assert. https://lore.kernel.org/all/20260603015831.41664-1-yexun@linux.alibaba.com/ v2: Assert vaddr instead of pfn. https://lore.kernel.org/all/20260602060116.35206-1-yexun@linux.alibaba.com/ v1: https://lore.kernel.org/all/20260601035401.39303-1-yexun@linux.alibaba.com/ x86/lam.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/x86/lam.c b/x86/lam.c index 87efc5dd..63a36539 100644 --- a/x86/lam.c +++ b/x86/lam.c @@ -231,13 +231,13 @@ static void test_lam_user(void) bool has_lam = this_cpu_has(X86_FEATURE_LAM); /* - * The physical address of AREA_NORMAL is within 36 bits, so that using + * The physical address of AREA_LOW is within 36 bits, so that using * identical mapping, the linear address will be considered as user mode * address from the view of LAM, and the metadata bits are not used as * address for both LAM48 and LAM57. */ - vaddr = alloc_pages_flags(0, AREA_NORMAL); - static_assert((AREA_NORMAL_PFN & GENMASK(63, 47)) == 0UL); + vaddr = alloc_pages_flags(0, AREA_LOW); + assert(((u64)vaddr & GENMASK(63, 47)) == 0UL); /* * Note, LAM doesn't have a global control bit to turn on/off LAM -- 2.54.0