On 08/01/18 17:20, Boris Ostrovsky wrote: > On 01/08/2018 11:10 AM, Peter Zijlstra wrote: >> On Sat, Jan 06, 2018 at 01:39:48PM -0800, Nick Desaulniers wrote: >>> Variable Length Arrays In Structs (VLAIS) is not supported by Clang, and >>> frowned upon by others. >>> >>> https://lkml.org/lkml/2013/9/23/500 >>> >>> Here, the VLAIS was used because the size of the bitmap returned from >>> xen_mc_entry() depended on possibly (based on kernel configuration) >>> runtime sized data. Rather than declaring args as a VLAIS then calling >>> sizeof on *args, we calculate the appropriate sizeof args manually. >>> Further, we can get rid of the #ifdef's and rely on num_possible_cpus() >>> (thanks to a helpful checkpatch warning from an earlier version of this >>> patch). >>> >>> Suggested-by: Juergen Gross <jgr...@suse.com> >>> Signed-off-by: Nick Desaulniers <nick.desaulni...@gmail.com> >>> --- >>> Changes in v2: >>> * Change mask to us DECLARE_BITMAP instead of pointer, as suggested. >>> * Update commit message to remove mention of pointer. >>> * Update sizeof calculation to work with array rather than pointer. >>> >>> arch/x86/xen/mmu_pv.c | 8 +++----- >>> 1 file changed, 3 insertions(+), 5 deletions(-) >>> >>> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c >>> index 4d62c07..d850762 100644 >>> --- a/arch/x86/xen/mmu_pv.c >>> +++ b/arch/x86/xen/mmu_pv.c >>> @@ -1325,20 +1325,18 @@ static void xen_flush_tlb_others(const struct >>> cpumask *cpus, >>> { >>> struct { >>> struct mmuext_op op; >>> -#ifdef CONFIG_SMP >>> - DECLARE_BITMAP(mask, num_processors); >>> -#else >>> DECLARE_BITMAP(mask, NR_CPUS); >>> -#endif >>> } *args; >> Why is it OK for Xen to place this bitmap on-stack in the first place? >> That NR_CPUS thing can be fairly huge. > > Err... right. Now it's even worse than it was before, when the array was > potentially smaller. I'll drop this.
No, its only the pointer to the struct, not the struct itself. Juergen _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
