From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:57896 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728252AbgB0EDz (ORCPT ); Wed, 26 Feb 2020 23:03:55 -0500 Date: Wed, 26 Feb 2020 20:03:53 -0800 From: Andrew Morton Subject: Re: [PATCH V14] mm/debug: Add tests validating architecture page table helpers Message-Id: <20200226200353.ea5c8ec2efacfb1192f3f3f4@linux-foundation.org> In-Reply-To: <52db1e9b-83b3-c41f-ef03-0f43e2159a83@arm.com> References: <1581909460-19148-1-git-send-email-anshuman.khandual@arm.com> <1582726182.7365.123.camel@lca.pw> <1582726340.7365.124.camel@lca.pw> <52db1e9b-83b3-c41f-ef03-0f43e2159a83@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: linux-s390-owner@vger.kernel.org List-ID: To: Anshuman Khandual Cc: Christophe Leroy , Qian Cai , linux-mm@kvack.org, Mike Rapoport , Vineet Gupta , Catalin Marinas , Will Deacon , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , "Kirill A . Shutemov" , Paul Walmsley , Palmer Dabbelt , linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, James Morse On Thu, 27 Feb 2020 08:04:05 +0530 Anshuman Khandual wrote: > > Must be something wrong with the following in debug_vm_pgtable() > >=20 > > =A0=A0=A0=A0paddr =3D __pa(&start_kernel); > >=20 > > Is there any explaination why start_kernel() is not in linear memory on= ARM64 ? >=20 >=20 > Cc: + James Morse >=20 > This warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel sy= mbol > i.e 'start_kernel' which might be outside the linear map. This happens du= e to > kernel mapping position randomization with KASLR. Adding James here in ca= se he > might like to add more. >=20 > __pa_symbol() should have been used instead, for accessing the physical a= ddress > here. On arm64 __pa() does check for linear address with __is_lm_address(= ) and > switch accordingly if it is a kernel text symbol. Nevertheless, its much = better > to use __pa_symbol() here rather than __pa(). >=20 > Rather than respining the patch once more, will just send a fix replacing= this > helper __pa() with __pa_symbol() for Andrew to pick up as this patch is a= lready > part of linux-next (next-20200226). But can definitely respin if that wil= l be > preferred. I didn't see this fix? I assume it's this? If so, are we sure it's OK to = be added to -next without testing?? From: Andrew Morton Subject: mm-debug-add-tests-validating-architecture-page-table-helpers-fix A warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol i.e 'start_kernel' which might be outside the linear map. This happens due to kernel mapping position randomization with KASLR. __pa_symbol() should have been used instead, for accessing the physical address here. On arm64 __pa() does check for linear address with __is_lm_address() and switch accordingly if it is a kernel text symbol.=20 Nevertheless, its much better to use __pa_symbol() here rather than __pa(). Reported-by: Qian Cai Cc: Anshuman Khandual Cc: James Morse Cc: Christophe Leroy Signed-off-by: Andrew Morton --- mm/debug_vm_pgtable.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/debug_vm_pgtable.c~mm-debug-add-tests-validating-architecture-page= -table-helpers-fix +++ a/mm/debug_vm_pgtable.c @@ -331,7 +331,7 @@ void __init debug_vm_pgtable(void) * helps avoid large memory block allocations to be used for mapping * at higher page table levels. */ - paddr =3D __pa(&start_kernel); + paddr =3D __pa_symbol(&start_kernel); =20 pte_aligned =3D (paddr & PAGE_MASK) >> PAGE_SHIFT; pmd_aligned =3D (paddr & PMD_MASK) >> PAGE_SHIFT; _