linux-kernel - Re: [RFC 11/20] mm/tlb: remove arch-specific tlb_start/end

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]

Date:   Tue, 2 Feb 2021 09:54:36 +0000
From:   Nadav Amit <namit@...are.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Nicholas Piggin <npiggin@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, X86 ML <x86@...nel.org>,
        Yu Zhao <yuzhao@...gle.com>
Subject: Re: [RFC 11/20] mm/tlb: remove arch-specific tlb_start/end_vma()

> On Feb 2, 2021, at 1:31 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Tue, Feb 02, 2021 at 07:20:55AM +0000, Nadav Amit wrote:
>> Arm does not define tlb_end_vma, and consequently it flushes the TLB after
>> each VMA. I suspect it is not intentional.
> 
> ARM is one of those that look at the VM_EXEC bit to explicitly flush
> ITLB IIRC, so it has to.

Hmm… I don’t think Arm is doing that. At least arm64 does not use the
default tlb_flush(), and it does not seem to consider VM_EXEC (at least in
this path):

static inline void tlb_flush(struct mmu_gather *tlb)
{
        struct vm_area_struct vma = TLB_FLUSH_VMA(tlb->mm, 0);
        bool last_level = !tlb->freed_tables;
        unsigned long stride = tlb_get_unmap_size(tlb);
        int tlb_level = tlb_get_level(tlb);
        
        /*
         * If we're tearing down the address space then we only care about
         * invalidating the walk-cache, since the ASID allocator won't
         * reallocate our ASID without invalidating the entire TLB.
         */
        if (tlb->mm_exiting) {
                if (!last_level)
                        flush_tlb_mm(tlb->mm);
                return;
        }       
        
        __flush_tlb_range(&vma, tlb->start, tlb->end, stride,
                          last_level, tlb_level);
}