linux-kernel - Re: [PATCH UPDATE] x86: ignore spurious faults

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <200801251041.17392.nickpiggin@yahoo.com.au>
Date:	Fri, 25 Jan 2008 10:41:16 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Matt Mackall <mpm@...enic.com>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>
Subject: Re: [PATCH UPDATE] x86: ignore spurious faults

On Friday 25 January 2008 06:21, Jeremy Fitzhardinge wrote:
> Matt Mackall wrote:
> > There's perhaps an opportunity to do this lazy TLB trick in the mmap
> > path as well, where RW mappings are initially mapped as RO so we can
> > catch processes dirtying them and then switched to RW. If the mapping is
> > shared across threads on multiple cores, we can defer synchronizing the
> > TLBs on the others.
>
> I think spurious usermode faults are already dealt with.
> handle_pte_fault() does essentially the same thing as this patch:
>
> 	if (ptep_set_access_flags(vma, address, pte, entry, write_access)) {
> 		update_mmu_cache(vma, address, entry);
> 	} else {
> 		/*
> 		 * This is needed only for protection faults but the arch code
> 		 * is not yet telling us if this is a protection fault or not.
> 		 * This still avoids useless tlb flushes for .text page faults
> 		 * with threads.
> 		 */
> 		if (write_access)
> 			flush_tlb_page(vma, address);
> 	}

I (obviously) don't know exactly how the TLB works in x86, but I
thought that on a miss, the CPU walks the pagetables first before
faulting? Maybe that's not the case if there is an RO entry
actually in the TLB?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/