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Tue, 12 Oct 2021 03:16:31 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwkghYFByrZHWmiyuVaP/T5E/0uYqrI4d0vpEGa+/BuFxVaGcBXZCk9WyZp0G0JjIXp3aT0CA== X-Received: by 2002:a17:90a:7e82:: with SMTP id j2mr4937753pjl.165.1634033791509; Tue, 12 Oct 2021 03:16:31 -0700 (PDT) Received: from t490s ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id 197sm10449044pfv.6.2021.10.12.03.16.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Oct 2021 03:16:30 -0700 (PDT) Date: Tue, 12 Oct 2021 18:16:22 +0800 From: Peter Xu To: Nadav Amit Cc: Andrew Morton , LKML , Linux-MM , Nadav Amit , Andrea Arcangeli , Andrew Cooper , Andy Lutomirski , Dave Hansen , Peter Zijlstra , Thomas Gleixner , Will Deacon , Yu Zhao , Nick Piggin , x86@kernel.org Subject: Re: [PATCH 1/2] mm/mprotect: use mmu_gather Message-ID: References: <20210925205423.168858-1-namit@vmware.com> <20210925205423.168858-2-namit@vmware.com> MIME-Version: 1.0 In-Reply-To: <20210925205423.168858-2-namit@vmware.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: EA31F6001980 X-Stat-Signature: jfki8in9z3czcxr8jxmbn1yxiz8cqehc Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=YgNRPcPP; spf=none (imf10.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1634033794-992757 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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