All of lore.kernel.org
 help / color / mirror / Atom feed
From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH v2 08/14] x86/cpuid: Handle leaf 0x80000008 in guest_cpuid()
Date: Tue, 24 Jan 2017 15:31:21 +0000	[thread overview]
Message-ID: <a0eb90d5-ee52-76a1-9431-a69d210c5ae9@citrix.com> (raw)
In-Reply-To: <5887539202000078001334BD@prv-mh.provo.novell.com>

On 24/01/17 12:16, Jan Beulich wrote:
>>>> On 23.01.17 at 15:39, <andrew.cooper3@citrix.com> wrote:
>> AMD uses 24 bits in eax, although nothing thus far has ever exposed a non-zero
>> guest maxphysaddr to HVM guests.
> I think exposing bits 16...23 should be limited to guests with nested
> virt enabled, and should also be subject to bounds checking just
> like is done for maxphysaddr.

I am not actually sure what the purpose of this field is.  It is zero
when read by Xen, even on HAP-capable processors, and the AMD manuals
make no reference to it.  (The CPUID section refers to the entirety of
the SVM section, but the field isn't actually mentioned anywhere, even
in the nested paging subsection.)

I think it is intended to be filled in by the hypervisor for hap guests,
but I can't think of a situation where it would be useful to tell a
guest its HAP maxphysaddr differently to regular maxphysaddr.

Furthermore the field is explicitly documented as "if 0, refer to plain
maxphysaddr".  At the moment, nothing ever fill in a value other than 0.

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel

  reply	other threads:[~2017-01-24 15:31 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-23 14:39 [PATCH v2 00/14] x86/cpuid: Handling of simple leaves in guest_cpuid() Andrew Cooper
2017-01-23 14:39 ` [PATCH v2 01/14] x86/cpufeatures: Expose self-snoop to all guests Andrew Cooper
2017-01-24 11:08   ` Jan Beulich
2017-01-24 11:28   ` Roger Pau Monné
2017-01-23 14:39 ` [PATCH v2 02/14] x86/cpuid: Handle leaf 0x80000000 in guest_cpuid() Andrew Cooper
2017-01-23 14:39 ` [PATCH v2 03/14] x86/cpuid: Only recalculate the shared feature bits once Andrew Cooper
2017-01-23 14:39 ` [PATCH v2 04/14] x86/cpuid: Handle more simple Intel leaves in guest_cpuid() Andrew Cooper
2017-01-24 11:20   ` Jan Beulich
2017-01-24 11:35     ` Andrew Cooper
2017-01-24 11:44       ` Jan Beulich
2017-01-23 14:39 ` [PATCH v2 05/14] x86/cpuid: Handle leaf 0x80000001 " Andrew Cooper
2017-01-24 11:51   ` Jan Beulich
2017-01-23 14:39 ` [PATCH v2 06/14] x86/cpuid: Handle the long vendor string " Andrew Cooper
2017-01-23 14:39 ` [PATCH v2 07/14] x86/cpuid: Handle leaves 0x80000005-7 " Andrew Cooper
2017-01-24 11:59   ` Jan Beulich
2017-01-24 14:48     ` Andrew Cooper
2017-01-24 15:05       ` Jan Beulich
2017-01-24 15:32         ` Andrew Cooper
2017-01-23 14:39 ` [PATCH v2 08/14] x86/cpuid: Handle leaf 0x80000008 " Andrew Cooper
2017-01-24 12:16   ` Jan Beulich
2017-01-24 15:31     ` Andrew Cooper [this message]
2017-01-24 15:50       ` Jan Beulich
2017-01-24 15:58         ` Andrew Cooper
2017-01-24 16:30   ` [PATCH v3 " Andrew Cooper
2017-01-25  9:22     ` Jan Beulich
2017-01-23 14:39 ` [PATCH v2 09/14] x86/cpuid: Handle leaf 0x80000009 " Andrew Cooper
2017-01-24 12:16   ` Jan Beulich
2017-01-23 14:39 ` [PATCH v2 10/14] x86/cpuid: Handle leaf 0x8000000a " Andrew Cooper
2017-01-24 12:20   ` Jan Beulich
2017-01-23 14:39 ` [PATCH v2 11/14] x86/cpuid: Handle leaves 0x8000000b-1a " Andrew Cooper
2017-01-23 14:47   ` Wei Liu
2017-01-24 12:26   ` Jan Beulich
2017-01-24 16:00     ` Andrew Cooper
2017-01-24 16:31   ` [PATCH v3 " Andrew Cooper
2017-01-25  9:22     ` Jan Beulich
2017-01-23 14:39 ` [PATCH v2 12/14] x86/cpufeatures: Hide Instruction Based Sampling from guests Andrew Cooper
2017-01-24 12:43   ` Jan Beulich
2017-01-23 14:39 ` [PATCH v2 13/14] x86/cpuid: Handle leaf 0x8000001c in guest_cpuid() Andrew Cooper
2017-01-23 18:50   ` Boris Ostrovsky
2017-01-24 16:20   ` Jan Beulich
2017-01-23 14:39 ` [PATCH v2 14/14] x86/cpuid: Remove the legacy path handling extd leaves Andrew Cooper
2017-01-24 16:29   ` Jan Beulich

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=a0eb90d5-ee52-76a1-9431-a69d210c5ae9@citrix.com \
    --to=andrew.cooper3@citrix.com \
    --cc=JBeulich@suse.com \
    --cc=xen-devel@lists.xen.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.