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Mon, 2 Nov 2026 12:32:58 -0500 (EST) Date: Mon, 2 Nov 2026 17:32:56 +0000 From: Kiryl Shutsemau To: "Edgecombe, Rick P" Cc: "peterz@infradead.org" , "luto@kernel.org" , "dave.hansen@linux.intel.com" , "andrew+kernel@donnellan.id.au" , "rppt@kernel.org" , "pasha.tatashin@soleen.com" , "kernel-team@meta.com" , "akpm@linux-foundation.org" , "david@kernel.org" , "mingo@redhat.com" , "linux-kernel@vger.kernel.org" , "peterx@redhat.com" , "tj@kernel.org" , "azpijr@gmail.com" , "linux-mm@kvack.org" , "hpa@zytor.com" , "baolin.wang@linux.alibaba.com" , "tglx@kernel.org" , "rmclure@linux.ibm.com" , "bp@alien8.de" , "x86@kernel.org" Subject: Re: [PATCH] x86/mm: Define the zapped-entry checks only with CONFIG_DEBUG_VM Message-ID: References: <20261102144001.342837-1-kas@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: w96ww7j83ihsppk43bztw4wkjfer4477 X-Rspamd-Queue-Id: 6E40F40003 X-Rspam-User: X-Rspamd-Server: rspam08 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793640787-367574 X-HE-Meta: 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 km8rqFAa 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Mon, Nov 02, 2026 at 04:53:17PM +0000, Edgecombe, Rick P wrote: > Do you happen to know if this performance impact is relevant at all in the non > Safe RET case? Yes, both sides of the comparison are the same kernel with Safe RET on, with and without the patch. Without Safe RET (spec_rstack_overflow=off, same two kernels) the call and return predict fine: branch misses are the same with and without the patch, and the gain is under 2%, within noise. > > diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c > > index 4a105f283cfb..3352bc6904f3 100644 > > --- a/arch/x86/mm/pgtable.c > > +++ b/arch/x86/mm/pgtable.c > > @@ -798,6 +798,7 @@ pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma) > >   return pmd_clear_saveddirty(pmd); > >  } > >   > > +#ifdef CONFIG_DEBUG_VM > >  void arch_check_zapped_pte(struct vm_area_struct *vma, pte_t pte) > >  { > >   /* > > @@ -823,3 +824,4 @@ void arch_check_zapped_pud(struct vm_area_struct *vma, > > pud_t pud) > >   /* See note in arch_check_zapped_pte() */ > >   VM_WARN_ON_ONCE(!(vma->vm_flags & VM_SHADOW_STACK) && > > pud_shstk(pud)); > > I guess all of these don't need to be the "VM_WARN_" varieties if they are > compiled out in the other case. I can do either way. It is functionally equivalent. -- Kiryl Shutsemau / Kirill A. Shutemov