linux-kernel - Re: [PATCH v3 1/4] x86/vm86/32: Switch to flush_tlb_mm_range() in mark_screen

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Date:   Thu, 27 Apr 2017 00:02:41 +0000
From:   Nadav Amit <namit@...are.com>
To:     Andy Lutomirski <luto@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Borislav Petkov" <bp@...en8.de>, Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Michal Hocko <mhocko@...e.com>,
        Sasha Levin <sasha.levin@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 1/4] x86/vm86/32: Switch to flush_tlb_mm_range() in
 mark_screen_rdonly()

And besides, it looks as if the code was meant to flush the entire
TLB in some cases (e.g., if pgd_none_or_clear_bad() is true).

On 4/26/17, 4:56 PM, "Nadav Amit" <namit@...are.com> wrote:

    It may be benign, but I don’t think that flushing the TLB without
    holding the ptl or the mmap_sem (for no apparent reason) is a good
    practice.
    
    On 4/22/17, 12:01 AM, "Andy Lutomirski" <luto@...nel.org> wrote:
    
        mark_screen_rdonly() is the last remaining caller of flush_tlb().
        flush_tlb_mm_range() is potentially faster and isn't obsolete.
        
        Compile-tested only because I don't know whether software that uses
        this mechanism even exists.
        
        Cc: Rik van Riel <riel@...hat.com>
        Cc: Dave Hansen <dave.hansen@...el.com>
        Cc: Nadav Amit <namit@...are.com>
        Cc: Michal Hocko <mhocko@...e.com>
        Cc: Sasha Levin <sasha.levin@...cle.com>
        Cc: Andrew Morton <akpm@...ux-foundation.org>
        Signed-off-by: Andy Lutomirski <luto@...nel.org>
        ---
         arch/x86/kernel/vm86_32.c | 2 +-
         1 file changed, 1 insertion(+), 1 deletion(-)
        
        diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
        index 23ee89ce59a9..3eda76b3c835 100644
        --- a/arch/x86/kernel/vm86_32.c
        +++ b/arch/x86/kernel/vm86_32.c
        @@ -193,7 +193,7 @@ static void mark_screen_rdonly(struct mm_struct *mm)
         	pte_unmap_unlock(pte, ptl);
         out:
         	up_write(&mm->mmap_sem);
        -	flush_tlb();
        +	flush_tlb_mm_range(mm, 0xA0000, 0xA0000 + 32*PAGE_SIZE, 0UL);
         }
         
         
        -- 
        2.9.3