From: Wei Liu <wei.liu2@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Tim Deegan <tim@xen.org>,
Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wei.liu2@citrix.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
xen-devel@lists.xen.org, Chao Gao <chao.gao@intel.com>
Subject: Re: [RFC Patch v4 8/8] x86/hvm: bump the maximum number of vcpus to 512
Date: Fri, 23 Feb 2018 17:18:47 +0000 [thread overview]
Message-ID: <20180223171847.7hojepjezcymbgbt@citrix.com> (raw)
In-Reply-To: <5A8FE3CD02000078001AABEB@prv-mh.provo.novell.com>
On Fri, Feb 23, 2018 at 01:50:05AM -0700, Jan Beulich wrote:
> >>> On 22.02.18 at 19:46, <wei.liu2@citrix.com> wrote:
> > On Wed, Dec 06, 2017 at 03:50:14PM +0800, Chao Gao wrote:
> >> --- a/xen/include/public/hvm/hvm_info_table.h
> >> +++ b/xen/include/public/hvm/hvm_info_table.h
> >> @@ -32,7 +32,7 @@
> >> #define HVM_INFO_PADDR ((HVM_INFO_PFN << 12) + HVM_INFO_OFFSET)
> >>
> >> /* Maximum we can support with current vLAPIC ID mapping. */
> >> -#define HVM_MAX_VCPUS 128
> >> +#define HVM_MAX_VCPUS 512
> >
> > I checked a few places where this is used, bumping the number doesn't
> > seem to be harmful on the surface.
> >
> > Of course there is the question how many CPUs can upstream support,
> > I think it is still under argument at the moment.
>
> Leaving the latter aside, it is never okay to simply change a #define
> in the public interface. See e.g. fb442e2171 ("x86_64: allow more
> vCPU-s per guest"), where we've already gone a somewhat harsh
> route by dropping the original #define altogether (thus at least
> causing build failures for consumers), taking the position that it
> wasn't correct to expose the value in the first place.
>
> Hence at the very least I can't see how struct hvm_info_table
> (in the same public header) can be left alone with this change.
AIUI this change has made the structure larger by extending the trailing
array. The resulting structure still fits into one page. At least to me
the new ABI is still compatible with the old.
The commit you mentioned is different because it completely breaks ABI
compatibility.
Wei.
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next prev parent reply other threads:[~2018-02-23 17:18 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-06 7:50 [RFC Patch v4 0/8] Extend resources to support more vcpus in single VM Chao Gao
2017-12-06 7:50 ` [RFC Patch v4 1/8] ioreq: remove most 'buf' parameter from static functions Chao Gao
2017-12-06 14:44 ` Paul Durrant
2017-12-06 8:37 ` Chao Gao
2017-12-06 7:50 ` [RFC Patch v4 2/8] ioreq: bump the number of IOREQ page to 4 pages Chao Gao
2017-12-06 15:04 ` Paul Durrant
2017-12-06 9:02 ` Chao Gao
2017-12-06 16:10 ` Paul Durrant
2017-12-07 8:41 ` Paul Durrant
2017-12-07 6:56 ` Chao Gao
2017-12-08 11:06 ` Paul Durrant
2017-12-12 1:03 ` Chao Gao
2017-12-12 9:07 ` Paul Durrant
2017-12-12 23:39 ` Chao Gao
2017-12-13 10:49 ` Paul Durrant
2017-12-13 17:50 ` Paul Durrant
2017-12-14 14:50 ` Paul Durrant
2017-12-15 0:35 ` Chao Gao
2017-12-15 9:40 ` Paul Durrant
2018-04-18 8:19 ` Jan Beulich
2017-12-06 7:50 ` [RFC Patch v4 3/8] xl/acpi: unify the computation of lapic_id Chao Gao
2018-02-22 18:05 ` Wei Liu
2017-12-06 7:50 ` [RFC Patch v4 4/8] hvmloader: boot cpu through broadcast Chao Gao
2018-02-22 18:44 ` Wei Liu
2018-02-23 8:41 ` Jan Beulich
2018-02-23 16:42 ` Roger Pau Monné
2018-02-24 5:49 ` Chao Gao
2018-02-26 8:28 ` Jan Beulich
2018-02-26 12:33 ` Chao Gao
2018-02-26 14:19 ` Roger Pau Monné
2018-04-18 8:38 ` Jan Beulich
2018-04-18 11:20 ` Chao Gao
2018-04-18 11:50 ` Jan Beulich
2017-12-06 7:50 ` [RFC Patch v4 5/8] Tool/ACPI: DSDT extension to support more vcpus Chao Gao
2017-12-06 7:50 ` [RFC Patch v4 6/8] hvmload: Add x2apic entry support in the MADT and SRAT build Chao Gao
2018-04-18 8:48 ` Jan Beulich
2017-12-06 7:50 ` [RFC Patch v4 7/8] x86/hvm: bump the number of pages of shadow memory Chao Gao
2018-02-27 14:17 ` George Dunlap
2018-04-18 8:53 ` Jan Beulich
2018-04-18 11:39 ` Chao Gao
2018-04-18 11:50 ` Andrew Cooper
2018-04-18 11:59 ` Jan Beulich
2017-12-06 7:50 ` [RFC Patch v4 8/8] x86/hvm: bump the maximum number of vcpus to 512 Chao Gao
2018-02-22 18:46 ` Wei Liu
2018-02-23 8:50 ` Jan Beulich
2018-02-23 17:18 ` Wei Liu [this message]
2018-02-23 18:11 ` Roger Pau Monné
2018-02-24 6:26 ` Chao Gao
2018-02-26 8:26 ` Jan Beulich
2018-02-26 13:11 ` Chao Gao
2018-02-26 16:10 ` Jan Beulich
2018-03-01 5:21 ` Chao Gao
2018-03-01 7:17 ` Juergen Gross
2018-03-01 7:37 ` Jan Beulich
2018-03-01 7:11 ` Chao Gao
2018-02-27 14:59 ` George Dunlap
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