On Thu, Sep 10, 2026 at 01:23:15PM +0200, David Hildenbrand (Arm) wrote: > On 9/10/26 13:16, Yeoreum Yun wrote: > > On Thu, Sep 10, 2026 at 12:45:39PM +0200, David Hildenbrand (Arm) wrote: > >> On 9/10/26 12:31, Yeoreum Yun wrote: > >>> > >>> Well, users currently for using /proc/self/smaps are for check vm-flags: > >>> - guard-regions where using check_vmflags_guard() > >>> - pfnmap test where uses check_vmflag_pfnmap() > >> > >> Most vm-flags should not be an issue when it comes to merging. The only > >> exception are vmflags that do not prevent VMA merging. > >> > >> So it's VM_SOFTDIRTY and VM_MAYBE_GUARD. And I agree that for > >> guard-regions.c we > >> likely have to care such that we don't merge by accident with other VMAs > >> (guard > >> regions). > >> > >> But that's independent of memalign. > >> > >> ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PROT_WRITE, > >> 0, 0); > >> ASSERT_FALSE(check_vmflag_guard(ptr)); > >> > >> could be problematic on its own (unlikely but possible). > > > > Yes. That's why I'm think it would be good to use alloc_isolated_mem() > > in case of ANON mapping for this case. > > It's really only guest-region code that needs this. > > > > >> > >> For other flags, you really only have to find the smaps area that covers > >> the > >> given address and look at the vm-flags. > >> > >> Or am I missing something important? > >> > >> (merging vnas with VM_PFNMAP is impossible right now IIRC) > > > > No. what I want to say including the patch #3 is for the above case > > where you point out -- ASSERT_FALSE(check_vmflag_guard(ptr)). > > > > Since we don't have any interface to check vm_flags execpt smap > > and for memory mmaped with anon would have a chance to merge, > > We need something to replace memalign() with preventing unexpected VMA > > merge. > Only for the cases that actually really needs this, which is in my > understanding > guard-regions. > > And I repeat, this is not a memalign() problem.
Yes. I'm not claim memalign() is problem but want to prevent unwanted VMA merge. That's all. And as I mentioned in another reply, if we get rid of ASSERT_FALSE(check_vmflag_guard(ptr)), this patch would be droppable. -- Sincerely, Yeoreum Yun
