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Date: Thu, 9 May 2024 14:30:21 -0700
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Subject: Re: [PATCH 1/1] arch/fault: don't print logs for simulated poison
 errors
To: Axel Rasmussen <axelrasmussen@google.com>,
 Andrew Morton <akpm@linux-foundation.org>, Andy Lutomirski
 <luto@kernel.org>, "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>,
 Borislav Petkov <bp@alien8.de>,
 Christophe Leroy <christophe.leroy@csgroup.eu>,
 Dave Hansen <dave.hansen@linux.intel.com>,
 David Hildenbrand <david@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
 Helge Deller <deller@gmx.de>, Ingo Molnar <mingo@redhat.com>,
 "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
 Liu Shixin <liushixin2@huawei.com>,
 "Matthew Wilcox (Oracle)" <willy@infradead.org>,
 Michael Ellerman <mpe@ellerman.id.au>, Muchun Song <muchun.song@linux.dev>,
 "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
 Nicholas Piggin <npiggin@gmail.com>, Oscar Salvador <osalvador@suse.de>,
 Peter Xu <peterx@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
 Suren Baghdasaryan <surenb@google.com>, Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
 linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org
References: <20240509203907.504891-1-axelrasmussen@google.com>
 <20240509203907.504891-2-axelrasmussen@google.com>
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From: John Hubbard <jhubbard@nvidia.com>
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On 5/9/24 1:39 PM, Axel Rasmussen wrote:
> For real MCEs, various architectures print log messages when poisoned
> memory is accessed (which results in a SIGBUS). These messages can be
> important for users to understand the issue.
> 
> On the other hand, we have the userfaultfd UFFDIO_POISON operation,
> which can "simulate" memory poisoning. That particular process will get
> SIGBUS on access to the memory, but this effect is tied to an MM, rather
> than being global like a real poison event. So, we don't want to log
> about this case to the global kernel log; instead, let the process
> itself log or whatever else it wants to do. This avoids spamming the
> kernel log, and avoids e.g. drowning out real events with simulated
> ones.
> 
> To identify this situation, add a new VM_FAULT_HWPOISON_SIM flag. This
> is expected to be set *in addition to* one of the existing
> VM_FAULT_HWPOISON or VM_FAULT_HWPOISON_LARGE flags (which are mutually
> exclusive).
> 
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
> ---
>   arch/parisc/mm/fault.c   | 7 +++++--
>   arch/powerpc/mm/fault.c  | 6 ++++--
>   arch/x86/mm/fault.c      | 6 ++++--
>   include/linux/mm_types.h | 5 +++++
>   mm/hugetlb.c             | 3 ++-
>   mm/memory.c              | 2 +-
>   6 files changed, 21 insertions(+), 8 deletions(-)
> 

This completely fixes the uffd-unit-test behavior, I just did a quick
test run to be sure as well.

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard
NVIDIA


> diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
> index c39de84e98b0..e5370bcadf27 100644
> --- a/arch/parisc/mm/fault.c
> +++ b/arch/parisc/mm/fault.c
> @@ -400,9 +400,12 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
>   #ifdef CONFIG_MEMORY_FAILURE
>   		if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
>   			unsigned int lsb = 0;
> -			printk(KERN_ERR
> +
> +			if (!(fault & VM_FAULT_HWPOISON_SIM)) {
> +				pr_err(
>   	"MCE: Killing %s:%d due to hardware memory corruption fault at %08lx\n",
> -			tsk->comm, tsk->pid, address);
> +				tsk->comm, tsk->pid, address);
> +			}
>   			/*
>   			 * Either small page or large page may be poisoned.
>   			 * In other words, VM_FAULT_HWPOISON_LARGE and
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 53335ae21a40..ac5e8a3c7fba 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -140,8 +140,10 @@ static int do_sigbus(struct pt_regs *regs, unsigned long address,
>   	if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
>   		unsigned int lsb = 0; /* shutup gcc */
>   
> -		pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
> -			current->comm, current->pid, address);
> +		if (!(fault & VM_FAULT_HWPOISON_SIM)) {
> +			pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
> +				current->comm, current->pid, address);
> +		}
>   
>   		if (fault & VM_FAULT_HWPOISON_LARGE)
>   			lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index e4f3c7721f45..16d077a3ad14 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -928,9 +928,11 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
>   		struct task_struct *tsk = current;
>   		unsigned lsb = 0;
>   
> -		pr_err_ratelimited(
> +		if (!(fault & VM_FAULT_HWPOISON_SIM)) {
> +			pr_err_ratelimited(
>   	"MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
> -			tsk->comm, tsk->pid, address);
> +				tsk->comm, tsk->pid, address);
> +		}
>   		if (fault & VM_FAULT_HWPOISON_LARGE)
>   			lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
>   		if (fault & VM_FAULT_HWPOISON)
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 5240bd7bca33..7f8fc3efc5b2 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -1226,6 +1226,9 @@ typedef __bitwise unsigned int vm_fault_t;
>    * @VM_FAULT_HWPOISON_LARGE:	Hit poisoned large page. Index encoded
>    *				in upper bits
>    * @VM_FAULT_SIGSEGV:		segmentation fault
> + * @VM_FAULT_HWPOISON_SIM	Hit poisoned, PTE marker; this indicates a
> + *				simulated poison (e.g. via usefaultfd's
> + *                              UFFDIO_POISON), not a "real" hwerror.
>    * @VM_FAULT_NOPAGE:		->fault installed the pte, not return page
>    * @VM_FAULT_LOCKED:		->fault locked the returned page
>    * @VM_FAULT_RETRY:		->fault blocked, must retry
> @@ -1245,6 +1248,7 @@ enum vm_fault_reason {
>   	VM_FAULT_HWPOISON       = (__force vm_fault_t)0x000010,
>   	VM_FAULT_HWPOISON_LARGE = (__force vm_fault_t)0x000020,
>   	VM_FAULT_SIGSEGV        = (__force vm_fault_t)0x000040,
> +	VM_FAULT_HWPOISON_SIM   = (__force vm_fault_t)0x000080,
>   	VM_FAULT_NOPAGE         = (__force vm_fault_t)0x000100,
>   	VM_FAULT_LOCKED         = (__force vm_fault_t)0x000200,
>   	VM_FAULT_RETRY          = (__force vm_fault_t)0x000400,
> @@ -1270,6 +1274,7 @@ enum vm_fault_reason {
>   	{ VM_FAULT_HWPOISON,            "HWPOISON" },	\
>   	{ VM_FAULT_HWPOISON_LARGE,      "HWPOISON_LARGE" },	\
>   	{ VM_FAULT_SIGSEGV,             "SIGSEGV" },	\
> +	{ VM_FAULT_HWPOISON_SIM,	"HWPOISON_SIM" },	\
>   	{ VM_FAULT_NOPAGE,              "NOPAGE" },	\
>   	{ VM_FAULT_LOCKED,              "LOCKED" },	\
>   	{ VM_FAULT_RETRY,               "RETRY" },	\
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 65456230cc71..2b4e0173e806 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6485,7 +6485,8 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>   				pte_marker_get(pte_to_swp_entry(entry));
>   
>   			if (marker & PTE_MARKER_POISONED) {
> -				ret = VM_FAULT_HWPOISON_LARGE |
> +				ret = VM_FAULT_HWPOISON_SIM |
> +				      VM_FAULT_HWPOISON_LARGE |
>   				      VM_FAULT_SET_HINDEX(hstate_index(h));
>   				goto out_mutex;
>   			}
> diff --git a/mm/memory.c b/mm/memory.c
> index d2155ced45f8..29a833b996ae 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3910,7 +3910,7 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
>   
>   	/* Higher priority than uffd-wp when data corrupted */
>   	if (marker & PTE_MARKER_POISONED)
> -		return VM_FAULT_HWPOISON;
> +		return VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_SIM;
>   
>   	if (pte_marker_entry_uffd_wp(entry))
>   		return pte_marker_handle_uffd_wp(vmf);