From: David Hildenbrand <david@redhat.com>
To: Nadav Amit <nadav.amit@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Peter Xu <peterx@redhat.com>,
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 2/2] mm/mprotect: do not flush on permission promotion
Date: Thu, 7 Oct 2021 14:13:00 +0200 [thread overview]
Message-ID: <5485fae5-3cd6-9dc3-0579-dc8aab8a3de1@redhat.com> (raw)
In-Reply-To: <20210925205423.168858-3-namit@vmware.com>
On 25.09.21 22:54, Nadav Amit wrote:
> From: Nadav Amit <namit@vmware.com>
>
> Currently, using mprotect() to unprotect a memory region or uffd to
> unprotect a memory region causes a TLB flush. At least on x86, as
> protection is promoted, no TLB flush is needed.
>
> Add an arch-specific pte_may_need_flush() which tells whether a TLB
> flush is needed based on the old PTE and the new one. Implement an x86
> pte_may_need_flush().
>
> For x86, PTE protection promotion or changes of software bits does
> require a flush, also add logic that considers the dirty-bit. Changes to
> the access-bit do not trigger a TLB flush, although architecturally they
> should, as Linux considers the access-bit as a hint.
Is the added LOC worth the benefit? IOW, do we have some benchmark that
really benefits from that?
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-10-07 12:13 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
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 [this message]
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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