On Thu, 26 Jun 2025 15:47:36 +0300 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > On Thu, Jun 26, 2025 at 11:35:21AM +0200, Vegard Nossum wrote: > > > > On 26/06/2025 11:22, Vegard Nossum wrote: > > > > > > On 25/06/2025 14:50, Kirill A. Shutemov wrote: > > > > Linear Address Space Separation (LASS) is a security feature that > > > > intends to > > > > prevent malicious virtual address space accesses across user/kernel mode. > > > > > > I applied these patches on top of tip/master and when I try to boot it > > > fails with errno 12 (ENOMEM - Cannot allocate memory): > > > > > > [ 1.517526] Kernel panic - not syncing: Requested init /bin/bash > > > failed (error -12). > > For some reason, I failed to reproduce it. What is your toolchain? > > > > Just using standard defconfig and booting in qemu/KVM with 2G RAM. > > > > > > Bisect lands on "x86/asm: Introduce inline memcpy and memset". > > > > I think the newly added mulq to rep_stos_alternative clobbers %rdx, > > Yes, it makes sense. > > > at > > least this patch fixed it for me: > > > > diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h > > index 5cd0f18a431fe..bc096526432a1 100644 > > --- a/arch/x86/include/asm/string.h > > +++ b/arch/x86/include/asm/string.h > > @@ -28,7 +28,7 @@ static __always_inline void *__inline_memcpy(void *to, > > const void *from, size_t > > "2:\n\t" > > _ASM_EXTABLE_UA(1b, 2b) > > :"+c" (len), "+D" (to), "+S" (from), > > ASM_CALL_CONSTRAINT > > - : : "memory", _ASM_AX); > > + : : "memory", _ASM_AX, _ASM_DX); > > > > return ret + len; > > } > > This part is not needed. rep_movs_alternative() doesn't touch RDX. > > I will fold the patch below. > > Or maybe some asm guru can suggest a better way to fix it without > clobbering RDX? Or separate out the code where the value is a compile-time zero. That is pretty much 99% of the calls. David
