From: Jeremy Fitzhardinge <jeremy@goop.org>
To: weiming <zephyr.zhao@gmail.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
Subject: Re: a quick question about _PAGE_GLOBAL flag in para virt mode
Date: Sun, 15 Feb 2009 01:37:13 -0800 [thread overview]
Message-ID: <4997E249.1050407@goop.org> (raw)
In-Reply-To: <add59a3f0902141740j58f0223eu4d04a169885b6f54@mail.gmail.com>
weiming wrote:
> Hi,
>
> I noticed that in adjust_guest_l1e() in arch/x86/mm.c, _PAGE_GLOBAL
> flag is set for guest's non-kernel pages. Meanwhile,
> _PAGE_GUEST_KERNEL page cannot have the Global bit set.
>
> What's the purpose of setting Global bit for guest's user pages?
> AFAIK, when the Global bit is set, it prevents those entries be
> flushed from TLB. So it makes more sense to set it for guest's kernel
> pages.
In 64-bit, syscalls must go via Xen, which entails a cr3 reload. This
would normally flush the tlb, but since the usermode pages are global,
they remain in the tlb during the user->xen->kernel->xen->user transition.
J
next prev parent reply other threads:[~2009-02-15 9:37 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-15 1:40 a quick question about _PAGE_GLOBAL flag in para virt mode weiming
2009-02-15 9:37 ` Jeremy Fitzhardinge [this message]
2009-02-15 17:30 ` weiming
2009-02-15 22:26 ` Jeremy Fitzhardinge
2009-02-15 23:06 ` John Levon
2009-02-16 0:47 ` weiming
2009-02-16 2:35 ` How to disconnect a network card in the Virtual machine? ANNIE LI
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