From: Peter Xu <peterx@redhat.com>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Nadav Amit <namit@vmware.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
Nick Piggin <npiggin@gmail.com>,
x86@kernel.org
Subject: Re: [PATCH 1/2] mm/mprotect: use mmu_gather
Date: Tue, 12 Oct 2021 18:16:22 +0800 [thread overview]
Message-ID: <YWVgdmKIFnZcgjeY@t490s> (raw)
In-Reply-To: <20210925205423.168858-2-namit@vmware.com>
On Sat, Sep 25, 2021 at 01:54:22PM -0700, Nadav Amit wrote:
> @@ -338,25 +344,25 @@ static unsigned long change_protection_range(struct vm_area_struct *vma,
> struct mm_struct *mm = vma->vm_mm;
> pgd_t *pgd;
> unsigned long next;
> - unsigned long start = addr;
> unsigned long pages = 0;
> + struct mmu_gather tlb;
>
> BUG_ON(addr >= end);
> pgd = pgd_offset(mm, addr);
> flush_cache_range(vma, addr, end);
> inc_tlb_flush_pending(mm);
> + tlb_gather_mmu(&tlb, mm);
> + tlb_start_vma(&tlb, vma);
Pure question:
I actually have no idea why tlb_start_vma() is needed here, as protection range
can be just a single page, but anyway.. I do see that tlb_start_vma() contains
a whole-vma flush_cache_range() when the arch needs it, then does it mean that
besides the inc_tlb_flush_pending() to be dropped, so as to the other call to
flush_cache_range() above?
> do {
> next = pgd_addr_end(addr, end);
> if (pgd_none_or_clear_bad(pgd))
> continue;
> - pages += change_p4d_range(vma, pgd, addr, next, newprot,
> + pages += change_p4d_range(&tlb, vma, pgd, addr, next, newprot,
> cp_flags);
> } while (pgd++, addr = next, addr != end);
>
> - /* Only flush the TLB if we actually modified any entries: */
> - if (pages)
> - flush_tlb_range(vma, start, end);
> - dec_tlb_flush_pending(mm);
> + tlb_end_vma(&tlb, vma);
> + tlb_finish_mmu(&tlb);
>
> return pages;
> }
> --
> 2.25.1
>
--
Peter Xu
next prev parent reply other threads:[~2021-10-12 10:16 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-25 20:54 [PATCH 0/2] mm/mprotect: avoid unnecessary TLB flushes Nadav Amit
2021-09-25 20:54 ` [PATCH 1/2] mm/mprotect: use mmu_gather Nadav Amit
2021-10-03 12:10 ` Peter Zijlstra
2021-10-04 19:24 ` Nadav Amit
2021-10-05 6:53 ` Peter Zijlstra
2021-10-05 16:34 ` Nadav Amit
2021-10-11 3:45 ` Nadav Amit
2021-10-12 10:16 ` Peter Xu [this message]
2021-10-12 17:31 ` Nadav Amit
2021-10-12 23:20 ` Peter Xu
2021-10-13 15:59 ` Nadav Amit
2021-09-25 20:54 ` [PATCH 2/2] mm/mprotect: do not flush on permission promotion Nadav Amit
2021-10-07 12:13 ` David Hildenbrand
2021-10-07 16:16 ` Nadav Amit
2021-10-07 17:07 ` David Hildenbrand
2021-10-08 6:06 ` Nadav Amit
2021-10-08 7:35 ` David Hildenbrand
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