Re: [PATCH 6.6 000/389] 6.6.76-rc2 review

[Catalin Marinas <catalin.marinas@arm.com>]

On Wed, Feb 19, 2025 at 02:00:27PM +0000, Catalin Marinas wrote:
> > On Sat, 8 Feb 2025 at 16:54, Naresh Kamboju <naresh.kamboju@linaro.org> wrote:
> > > Regression on qemu-arm64 and FVP noticed this kernel warning running
> > > selftests: arm64: check_hugetlb_options test case on 6.6.76-rc1 and
> > > 6.6.76-rc2.
> > >
> > > Test regression: WARNING-arch-arm64-mm-copypage-copy_highpage
> > >
> > > ------------[ cut here ]------------
> > > [   96.920028] WARNING: CPU: 1 PID: 3611 at
> > > arch/arm64/mm/copypage.c:29 copy_highpage
> > > (arch/arm64/include/asm/mte.h:87)
> > > [   96.922100] Modules linked in: crct10dif_ce sm3_ce sm3 sha3_ce
> > > sha512_ce sha512_arm64 fuse drm backlight ip_tables x_tables
> > > [   96.925603] CPU: 1 PID: 3611 Comm: check_hugetlb_o Not tainted 6.6.76-rc2 #1
> > > [   96.926956] Hardware name: linux,dummy-virt (DT)
> > > [   96.927695] pstate: 43402009 (nZcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
> > > [   96.928687] pc : copy_highpage (arch/arm64/include/asm/mte.h:87)
> > > [   96.929037] lr : copy_highpage
> > > (arch/arm64/include/asm/alternative-macros.h:232
> > > arch/arm64/include/asm/cpufeature.h:443
> > > arch/arm64/include/asm/cpufeature.h:504
> > > arch/arm64/include/asm/cpufeature.h:814 arch/arm64/mm/copypage.c:27)
> > > [   96.929399] sp : ffff800088aa3ab0
> > > [   96.930232] x29: ffff800088aa3ab0 x28: 00000000000001ff x27: 0000000000000000
> > > [   96.930784] x26: 0000000000000000 x25: 0000ffff9b800000 x24: 0000ffff9b9ff000
> > > [   96.931402] x23: fffffc0003257fc0 x22: ffff0000c95ff000 x21: ffff0000c93ff000
> > > [   96.932054] x20: fffffc0003257fc0 x19: fffffc000324ffc0 x18: 0000ffff9b800000
> > > [   96.933357] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
> > > [   96.934091] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
> > > [   96.935095] x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
> > > [   96.935982] x8 : 0bfffc0001800000 x7 : 0000000000000000 x6 : 0000000000000000
> > > [   96.936536] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
> > > [   96.937089] x2 : 0000000000000000 x1 : ffff0000c9600000 x0 : ffff0000c9400080
> > > [   96.939431] Call trace:
> > > [   96.939920] copy_highpage (arch/arm64/include/asm/mte.h:87)
> > > [   96.940443] copy_user_highpage (arch/arm64/mm/copypage.c:40)
> > > [   96.940963] copy_user_large_folio (mm/memory.c:5977 mm/memory.c:6109)
> > > [   96.941535] hugetlb_wp (mm/hugetlb.c:5701)
> > > [   96.941948] hugetlb_fault (mm/hugetlb.c:6237)
> > > [   96.942344] handle_mm_fault (mm/memory.c:5330)
> > > [   96.942794] do_page_fault (arch/arm64/mm/fault.c:513
> > > arch/arm64/mm/fault.c:626)
> > > [   96.943341] do_mem_abort (arch/arm64/mm/fault.c:846)
> > > [   96.943797] el0_da (arch/arm64/kernel/entry-common.c:133
> > > arch/arm64/kernel/entry-common.c:144
> > > arch/arm64/kernel/entry-common.c:547)
> > > [   96.944229] el0t_64_sync_handler (arch/arm64/kernel/entry-common.c:0)
> > > [   96.944765] el0t_64_sync (arch/arm64/kernel/entry.S:599)
> > > [   96.945383] ---[ end trace 0000000000000000 ]---
> 
> Prior to commit 25c17c4b55de ("hugetlb: arm64: add mte support"), there
> was no hugetlb support with MTE, so the above code path should not
> happen - it seems to get a PROT_MTE hugetlb page which should have been
> prevented by arch_validate_flags(). Or something else corrupts the page
> flags and we end up with some random PG_mte_tagged set.

The problem is in the arm64 arch_calc_vm_flag_bits() as it returns
VM_MTE_ALLOWED for any MAP_ANONYMOUS ignoring MAP_HUGETLB (it's been
doing this since day 1 of MTE). The implementation does handle the
hugetlb file mmap() correctly but not the MAP_ANONYMOUS case.

The fix would be something like below:

-----------------8<--------------------------
diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index 5966ee4a6154..8ff5d88c9f12 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/arch/arm64/include/asm/mman.h
@@ -28,7 +28,8 @@ static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
 	 * backed by tags-capable memory. The vm_flags may be overridden by a
 	 * filesystem supporting MTE (RAM-based).
 	 */
-	if (system_supports_mte() && (flags & MAP_ANONYMOUS))
+	if (system_supports_mte() &&
+	    ((flags & MAP_ANONYMOUS) && !(flags & MAP_HUGETLB)))
 		return VM_MTE_ALLOWED;

 	return 0;
-------------------8<-----------------------

This fix won't make sense for mainline since it supports MAP_HUGETLB
already.

Greg, are you ok with a stable-only fix as above or you'd rather see the
full 25c17c4b55de ("hugetlb: arm64: add mte support") backported?

Thanks.

-- 
Catalin