From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: wei.liu2@citrix.com, George.Dunlap@eu.citrix.com,
Andrew Cooper <andrew.cooper3@citrix.com>,
ian.jackson@eu.citrix.com, Dario Faggioli <dfaggioli@suse.com>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH RFC v2 00/12] xen/x86: use per-vcpu stacks for 64 bit pv domains
Date: Tue, 23 Jan 2018 10:24:56 +0100 [thread overview]
Message-ID: <9392fbde-562c-5200-8b1c-33a737ed8972@suse.com> (raw)
In-Reply-To: <5A67061F02000078001A1669@suse.com>
On 23/01/18 09:53, Jan Beulich wrote:
>>>> On 23.01.18 at 07:34, <jgross@suse.com> wrote:
>> On 22/01/18 19:39, Andrew Cooper wrote:
>>> One of my concerns is that this patch series moves further away from the
>>> secondary goal of my KAISER series, which was to have the IDT and GDT
>>> mapped at the same linear addresses on every CPU so a) SIDT/SGDT don't
>>> leak which CPU you're currently scheduled on into PV guests and b) the
>>> context switch code can drop a load of its slow instructions like LGDT
>>> and the VMWRITEs to update the VMCS.
>>
>> The GDT address of a PV vcpu is depending on vcpu_id only. I don't
>> see why the IDT can't be mapped to the same address on each cpu with
>> my approach.
>
> You're not introducing a per-CPU range in the page tables afaics
> (again from overview and titles only), yet with the IDT needing
> to be per-CPU you'd also need a per-CPU range to map it to if
> you want to avoid the LIDT as well as exposing what CPU you're
> on (same goes for the GDT and the respective avoidance of LGDT
> afaict).
After a quick look I don't see why a Meltdown mitigation can't use
the same IDT for all cpus: the only reason I could find for having
per-cpu IDTs seems to be in SVM code, so it seems to be AMD specific.
And AMD won't need XPTI at all.
The GDT of pv domains is already in the per-domain region even without
my patches, so I don't have to change anything regarding usage of LGDT.
Juergen
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next prev parent reply other threads:[~2018-01-23 9:25 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-22 12:32 [PATCH RFC v2 00/12] xen/x86: use per-vcpu stacks for 64 bit pv domains Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 01/12] x86: cleanup processor.h Juergen Gross
2018-01-22 12:52 ` Jan Beulich
[not found] ` <5A65ECA502000078001A111C@suse.com>
2018-01-22 14:10 ` Juergen Gross
2018-01-22 14:25 ` Andrew Cooper
2018-01-22 14:32 ` Jan Beulich
2018-01-22 12:32 ` [PATCH RFC v2 02/12] x86: don't use hypervisor stack size for dumping guest stacks Juergen Gross
2018-01-23 9:26 ` Jan Beulich
[not found] ` <5A670DEF02000078001A16AF@suse.com>
2018-01-23 9:58 ` Juergen Gross
2018-01-23 10:11 ` Jan Beulich
[not found] ` <5A67187C02000078001A1742@suse.com>
2018-01-23 10:19 ` Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 03/12] x86: do a revert of e871e80c38547d9faefc6604532ba3e985e65873 Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 04/12] x86: revert 5784de3e2067ed73efc2fe42e62831e8ae7f46c4 Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 05/12] x86: don't access saved user regs via rsp in trap handlers Juergen Gross
2018-01-30 14:49 ` Jan Beulich
[not found] ` <5A70941B02000078001A3BF0@suse.com>
2018-01-30 16:33 ` Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 06/12] x86: add a xpti command line parameter Juergen Gross
2018-01-30 15:39 ` Jan Beulich
[not found] ` <5A709FDF02000078001A3C2C@suse.com>
2018-01-30 16:51 ` Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 07/12] x86: allow per-domain mappings without NX bit or with specific mfn Juergen Gross
2018-01-29 17:06 ` Jan Beulich
[not found] ` <5A6F62B602000078001A3810@suse.com>
2018-01-30 8:02 ` Juergen Gross
2018-01-30 8:41 ` Jan Beulich
2018-01-31 10:30 ` Jan Beulich
2018-01-22 12:32 ` [PATCH RFC v2 08/12] xen/x86: use dedicated function for tss initialization Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 09/12] x86: enhance syscall stub to work in per-domain mapping Juergen Gross
2018-01-30 15:11 ` Jan Beulich
[not found] ` <5A70991902000078001A3C16@suse.com>
2018-01-30 16:50 ` Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 10/12] x86: allocate per-vcpu stacks for interrupt entries Juergen Gross
2018-01-30 15:40 ` Jan Beulich
2018-02-09 12:35 ` Juergen Gross
2018-02-13 9:10 ` Jan Beulich
[not found] ` <5A70A01402000078001A3C30@suse.com>
2018-01-30 17:12 ` Juergen Gross
2018-01-31 10:18 ` Jan Beulich
2018-01-22 12:32 ` [PATCH RFC v2 11/12] x86: modify interrupt handlers to support stack switching Juergen Gross
2018-01-30 16:07 ` Jan Beulich
[not found] ` <5A70A63D02000078001A3C7C@suse.com>
2018-01-30 17:19 ` Juergen Gross
2018-01-31 10:36 ` Jan Beulich
[not found] ` <5A71AA4202000078001A3F56@suse.com>
2018-02-02 15:42 ` Juergen Gross
2018-01-22 12:32 ` [PATCH RFC v2 12/12] x86: activate per-vcpu stacks in case of xpti Juergen Gross
2018-01-30 16:33 ` Jan Beulich
[not found] ` <5A70AC7F02000078001A3CA6@suse.com>
2018-01-30 17:33 ` Juergen Gross
2018-01-31 10:40 ` Jan Beulich
2018-01-22 12:50 ` [PATCH RFC v2 00/12] xen/x86: use per-vcpu stacks for 64 bit pv domains Jan Beulich
[not found] ` <5A65EC0A02000078001A1118@suse.com>
2018-01-22 14:18 ` Juergen Gross
2018-01-22 14:22 ` Jan Beulich
[not found] ` <5A6601D302000078001A1230@suse.com>
2018-01-22 14:38 ` Juergen Gross
2018-01-22 14:48 ` Jan Beulich
[not found] ` <5A6607DB02000078001A127B@suse.com>
2018-01-22 15:00 ` Juergen Gross
2018-01-22 16:51 ` Jan Beulich
2018-01-22 18:39 ` Andrew Cooper
2018-01-22 18:48 ` George Dunlap
2018-01-22 19:02 ` Andrew Cooper
2018-01-23 8:36 ` Jan Beulich
2018-01-23 11:23 ` Andrew Cooper
2018-01-23 11:06 ` George Dunlap
2018-01-23 6:34 ` Juergen Gross
2018-01-23 7:21 ` Juergen Gross
2018-01-23 8:53 ` Jan Beulich
[not found] ` <5A67061F02000078001A1669@suse.com>
2018-01-23 9:24 ` Juergen Gross [this message]
2018-01-23 9:31 ` Jan Beulich
[not found] ` <5A670F0E02000078001A16C9@suse.com>
2018-01-23 10:10 ` Juergen Gross
2018-01-23 11:45 ` Andrew Cooper
2018-01-23 13:31 ` Juergen Gross
2018-01-23 13:24 ` Dario Faggioli
2018-01-23 16:45 ` George Dunlap
2018-01-23 16:56 ` Juergen Gross
2018-01-23 17:33 ` George Dunlap
2018-01-24 7:37 ` Jan Beulich
[not found] ` <5A6624A602000078001A1375@suse.com>
2018-01-23 5:50 ` Juergen Gross
2018-01-23 8:40 ` Jan Beulich
[not found] ` <5A67030F02000078001A164B@suse.com>
2018-01-23 9:45 ` Juergen Gross
2018-01-22 21:45 ` Konrad Rzeszutek Wilk
2018-01-23 6:38 ` Juergen Gross
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