Message ID | 20221205094817.21062-1-ayan.kumar.halder@amd.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [XEN,v4] xen/page_alloc: Relax the BUILD_BUG_ON() in xenheap_max_mfn() | expand |
On 05.12.2022 10:48, Ayan Kumar Halder wrote: > In the near future, we are considering to use a common xen/domain heap for > Arm 32-bit V8-R. In this setup, both PADDR_BITS and BITS_PER_LONG will be > 32. Therefore, the condition PADDR_BITS >= BITS_PER_LONG will become true. > > Looking at the commit that introduce the BUILD_BUG_ON (88e3ed61642b > "x86/NUMA: make init_node_heap() respect Xen heap limit") and the current > use, it seems this check was mainly to ensure that the shift of xenheap_bits > is not going to be undefined (>> N for a N-bit type is undefined). > > So far, all the shifts are using "xenheap_bits - PAGE_SHIFT". Therefore, the > existing code should work for 32-bit architecture as long as the result of > the substraction is below 32. > > Therefore relax the BUILD_BUG_ON() to check that (PADDR_BITS - PAGE_SHIFT) > is not equal of above BITS_PER_LONG. > > Note that we would need further precaution if we ended up to use > 'xenheap_bits' alone in shifts. > > Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com> > Signed-off-by: Julien Grall <julien@xen.org> Acked-by: Jan Beulich <jbeulich@suse.com>
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index 62afb07bc6..c5b8c7444f 100644 --- a/xen/common/page_alloc.c +++ b/xen/common/page_alloc.c @@ -2245,7 +2245,7 @@ void __init xenheap_max_mfn(unsigned long mfn) { ASSERT(!first_node_initialised); ASSERT(!xenheap_bits); - BUILD_BUG_ON(PADDR_BITS >= BITS_PER_LONG); + BUILD_BUG_ON((PADDR_BITS - PAGE_SHIFT) >= BITS_PER_LONG); xenheap_bits = min(flsl(mfn + 1) - 1 + PAGE_SHIFT, PADDR_BITS); printk(XENLOG_INFO "Xen heap: %u bits\n", xenheap_bits); }