From: "Jan Beulich" <JBeulich@suse.com>
To: Juergen Gross <jgross@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Tim Deegan <tim@xen.org>,
xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v7 1/9] x86/xpti: avoid copying L4 page table contents when possible
Date: Fri, 13 Apr 2018 02:43:15 -0600 [thread overview]
Message-ID: <5AD06DA302000078001BAFB0@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <20180412180944.31735-2-jgross@suse.com>
>>> On 12.04.18 at 20:09, <jgross@suse.com> wrote:
> For mitigation of Meltdown the current L4 page table is copied to the
> cpu local root page table each time a 64 bit pv guest is entered.
>
> Copying can be avoided in cases where the guest L4 page table hasn't
> been modified while running the hypervisor, e.g. when handling
> interrupts or any hypercall not modifying the L4 page table or %cr3.
>
> So add a per-cpu flag indicating whether the copying should be
> performed and set that flag only when loading a new %cr3 or modifying
> the L4 page table. This includes synchronization of the cpu local
> root page table with other cpus, so add a special synchronization flag
> for that case.
>
> A simple performance check (compiling the hypervisor via "make -j 4")
> in dom0 with 4 vcpus shows a significant improvement:
>
> - real time drops from 112 seconds to 103 seconds
> - system time drops from 142 seconds to 131 seconds
>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> ---
> V7:
> - add missing flag setting in shadow code
This now needs an ack from Tim (now Cc-ed).
Jan
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next prev parent reply other threads:[~2018-04-13 8:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-12 18:09 [PATCH v7 0/9] xen/x86: various XPTI speedups Juergen Gross
2018-04-12 18:09 ` [PATCH v7 1/9] x86/xpti: avoid copying L4 page table contents when possible Juergen Gross
2018-04-13 8:43 ` Jan Beulich [this message]
2018-04-16 15:34 ` Tim Deegan
2018-04-16 18:22 ` Juergen Gross
2018-04-18 6:55 ` Juergen Gross
2018-04-12 18:09 ` [PATCH v7 2/9] xen/x86: add a function for modifying cr3 Juergen Gross
2018-04-12 18:09 ` [PATCH v7 3/9] xen/x86: support per-domain flag for xpti Juergen Gross
2018-04-12 18:09 ` [PATCH v7 4/9] xen/x86: use invpcid for flushing the TLB Juergen Gross
2018-04-12 18:09 ` [PATCH v7 5/9] xen/x86: disable global pages for domains with XPTI active Juergen Gross
2018-04-12 18:09 ` [PATCH v7 6/9] xen/x86: use flag byte for decision whether xen_cr3 is valid Juergen Gross
2018-04-12 18:09 ` [PATCH v7 7/9] xen/x86: convert pv_guest_cr4_to_real_cr4() to a function Juergen Gross
2018-04-12 18:09 ` [PATCH v7 8/9] xen/x86: add some cr3 helpers Juergen Gross
2018-04-12 18:09 ` [PATCH v7 9/9] xen/x86: use PCID feature Juergen Gross
2018-04-13 9:59 ` [PATCH v7 0/9] xen/x86: various XPTI speedups Andrew Cooper
2018-04-13 10:29 ` Juergen Gross
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