Message-ID: <cd3c4a6a-abc5-4f4f-b829-72f86cfb5bde@redhat.com>
Date: Thu, 21 Aug 2025 14:52:06 +0200
From: David Hildenbrand <david@...hat.com>
To: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
 Anthony Yznaga <anthony.yznaga@...cle.com>, sparclinux@...r.kernel.org,
 davem@...emloft.net, andreas@...sler.com
Cc: linux-kernel@...r.kernel.org, agordeev@...ux.ibm.com, will@...nel.org,
 ryan.roberts@....com, osalvador@...e.de, Meelis Roos <mroos@...ux.ee>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: Re: Found it - was: Re: [PATCH] sparc64: fix hugetlb for sun4u

>>
>> @Anthony: Can you see any suspicious in the disassembled code that Meelis (CC'ed) posted?
> 
> OK, bisecting has lead me to the following commit:

CCing Rick.

Hm, but that's bpf-only code. Are you sure that it's this exact commit 
or rather ....

> 
> d53d2f78ceadba081fc7785570798c3c8d50a718 is the first bad commit
> commit d53d2f78ceadba081fc7785570798c3c8d50a718 (HEAD)
> Author: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Date:   Thu Apr 25 17:11:38 2019 -0700
> 
>      bpf: Use vmalloc special flag
>      
>      Use new flag VM_FLUSH_RESET_PERMS for handling freeing of special
>      permissioned memory in vmalloc and remove places where memory was set RW
>      before freeing which is no longer needed. Don't track if the memory is RO
>      anymore because it is now tracked in vmalloc.
>      
>      Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
>      Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>      Cc: <akpm@...ux-foundation.org>
>      Cc: <ard.biesheuvel@...aro.org>
>      Cc: <deneen.t.dock@...el.com>
>      Cc: <kernel-hardening@...ts.openwall.com>
>      Cc: <kristen@...ux.intel.com>
>      Cc: <linux_dti@...oud.com>
>      Cc: <will.deacon@....com>
>      Cc: Alexei Starovoitov <ast@...nel.org>
>      Cc: Andy Lutomirski <luto@...nel.org>
>      Cc: Borislav Petkov <bp@...en8.de>
>      Cc: Daniel Borkmann <daniel@...earbox.net>
>      Cc: Dave Hansen <dave.hansen@...ux.intel.com>
>      Cc: H. Peter Anvin <hpa@...or.com>
>      Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>      Cc: Nadav Amit <nadav.amit@...il.com>
>      Cc: Rik van Riel <riel@...riel.com>
>      Cc: Thomas Gleixner <tglx@...utronix.de>
>      Link: https://lkml.kernel.org/r/20190426001143.4983-19-namit@vmware.com
>      Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
>   include/linux/filter.h | 17 +++--------------
>   kernel/bpf/core.c      |  1 -
>   2 files changed, 3 insertions(+), 15 deletions(-)
> 
> I assume it's also related to this change:

... this one?

> 
> commit 868b104d7379e28013e9d48bdd2db25e0bdcf751
> Author: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Date:   Thu Apr 25 17:11:36 2019 -0700
> 
>      mm/vmalloc: Add flag for freeing of special permsissions
>      
>      Add a new flag VM_FLUSH_RESET_PERMS, for enabling vfree operations to
>      immediately clear executable TLB entries before freeing pages, and handle
>      resetting permissions on the directmap. This flag is useful for any kind
>      of memory with elevated permissions, or where there can be related
>      permissions changes on the directmap. Today this is RO+X and RO memory.
>      
>      Although this enables directly vfreeing non-writeable memory now,
>      non-writable memory cannot be freed in an interrupt because the allocation
>      itself is used as a node on deferred free list. So when RO memory needs to
>      be freed in an interrupt the code doing the vfree needs to have its own
>      work queue, as was the case before the deferred vfree list was added to
>      vmalloc.
>      
>      For architectures with set_direct_map_ implementations this whole operation
>      can be done with one TLB flush when centralized like this. For others with
>      directmap permissions, currently only arm64, a backup method using
>      set_memory functions is used to reset the directmap. When arm64 adds
>      set_direct_map_ functions, this backup can be removed.
>      
>      When the TLB is flushed to both remove TLB entries for the vmalloc range
>      mapping and the direct map permissions, the lazy purge operation could be
>      done to try to save a TLB flush later. However today vm_unmap_aliases
>      could flush a TLB range that does not include the directmap. So a helper
>      is added with extra parameters that can allow both the vmalloc address and
>      the direct mapping to be flushed during this operation. The behavior of the
>      normal vm_unmap_aliases function is unchanged.
>      
>      Suggested-by: Dave Hansen <dave.hansen@...el.com>
>      Suggested-by: Andy Lutomirski <luto@...nel.org>
>      Suggested-by: Will Deacon <will.deacon@....com>
>      Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
>      Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>      Cc: <akpm@...ux-foundation.org>
>      Cc: <ard.biesheuvel@...aro.org>
>      Cc: <deneen.t.dock@...el.com>
>      Cc: <kernel-hardening@...ts.openwall.com>
>      Cc: <kristen@...ux.intel.com>
>      Cc: <linux_dti@...oud.com>
>      Cc: Borislav Petkov <bp@...en8.de>
>      Cc: H. Peter Anvin <hpa@...or.com>
>      Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>      Cc: Nadav Amit <nadav.amit@...il.com>
>      Cc: Rik van Riel <riel@...riel.com>
>      Cc: Thomas Gleixner <tglx@...utronix.de>
>      Link: https://lkml.kernel.org/r/20190426001143.4983-17-namit@vmware.com
>      Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> Adrian
> 


-- 
Cheers

David / dhildenb

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