From: Juergen Gross <jgross@suse.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org
Subject: Re: [PATCH v3 09/11] x86/xen: use capabilities instead of fake cpuid values for xsave
Date: Mon, 24 Apr 2017 08:23:09 +0200 [thread overview]
Message-ID: <e60e4d87-8589-f22e-a5d0-a2d4e4b81d1c@suse.com> (raw)
In-Reply-To: <11745477-7dbb-cc36-1d14-f6cac9b0d13b@oracle.com>
On 21/04/17 16:51, Boris Ostrovsky wrote:
> On 04/21/2017 10:45 AM, Andrew Cooper wrote:
>> On 21/04/17 15:38, Juergen Gross wrote:
>>> On 21/04/17 16:24, Boris Ostrovsky wrote:
>>>>> +static bool __init xen_check_xsave(void)
>>>>> {
>>>>> - unsigned int ax, bx, cx, dx;
>>>>> - unsigned int xsave_mask;
>>>>> + unsigned int err, eax, edx;
>>>>>
>>>>> - ax = 1;
>>>>> - cx = 0;
>>>>> - cpuid(1, &ax, &bx, &cx, &dx);
>>>>> + /* Test OSXSAVE capability via xgetbv instruction. */
>>>>> + asm volatile("1: .byte 0x0f,0x01,0xd0\n\t" /* xgetbv */
>>>>> + "xor %[err], %[err]\n"
>>>>> + "2:\n\t"
>>>>> + ".pushsection .fixup,\"ax\"\n\t"
>>>>> + "3: movl $1,%[err]\n\t"
>>>>> + "jmp 2b\n\t"
>>>>> + ".popsection\n\t"
>>>>> + _ASM_EXTABLE(1b, 3b)
>>>>> + : [err] "=r" (err), "=a" (eax), "=d" (edx)
>>>>> + : "c" (0));
>>>> Have you tested this on processors where we actually trap on xgetbv?
>>>>
>>>> I have an AMD box without XSAVE support and this is a fatal error. I
>>>> suspect it's too early to use exception fixup framework here.
>>> Uuh, too bad.
>>>
>>> Then I fear we must use the other solution Andrew didn't like. :-(
>>> Andrew, would you be okay with that?
>> Hmm fine. The status quo is probably best then to unblock this series.
>>
>> As an independent question, why are exceptions set up so late? They
>> really should be the very first thing done
>
> It's exception fixup that is not set up yet --- we are executing here
> before "main" kernel's entry point.
>
> This is somewhat similar to what
> arch/x86/kernel/head_64.S:early_idt_handler_common() does --- it has
> special handling for early fixup --- early_fixup_exception().
>
> I wonder though --- can this feature masking be deferred until a bit later?
At least the xsave feature is tested rather early: it is needed in
early_cpu_init() being called way before trap_init().
Juergen
next prev parent reply other threads:[~2017-04-24 6:23 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-18 6:31 [PATCH v3 00/11] x86: xen cpuid() cleanup Juergen Gross
2017-04-18 6:31 ` [PATCH v3 01/11] xen: set cpu capabilities from xen_start_kernel() Juergen Gross
2017-04-18 6:31 ` [PATCH v3 02/11] x86/xen: don't indicate DCA support in pv domains Juergen Gross
2017-04-18 6:31 ` [PATCH v3 03/11] x86/xen: use capabilities instead of fake cpuid values for aperf Juergen Gross
2017-04-18 6:31 ` [PATCH v3 04/11] x86/xen: use capabilities instead of fake cpuid values for mtrr Juergen Gross
2017-04-18 6:31 ` [PATCH v3 05/11] x86/xen: use capabilities instead of fake cpuid values for acc Juergen Gross
2017-04-18 6:31 ` [PATCH v3 06/11] x86/xen: use capabilities instead of fake cpuid values for acpi Juergen Gross
2017-04-18 6:31 ` [PATCH v3 07/11] x86/xen: use capabilities instead of fake cpuid values for mwait Juergen Gross
2017-04-18 6:31 ` [PATCH v3 08/11] x86/xen: use capabilities instead of fake cpuid values for x2apic Juergen Gross
2017-04-18 6:31 ` [PATCH v3 09/11] x86/xen: use capabilities instead of fake cpuid values for xsave Juergen Gross
2017-04-18 10:02 ` [Xen-devel] " Andrew Cooper
2017-04-18 11:56 ` Juergen Gross
2017-04-21 14:24 ` Boris Ostrovsky
2017-04-21 14:38 ` Juergen Gross
2017-04-21 14:45 ` Andrew Cooper
2017-04-21 14:51 ` Boris Ostrovsky
2017-04-24 6:23 ` Juergen Gross [this message]
2017-04-18 6:31 ` [PATCH v3 10/11] vmware: set cpu capabilities during platform initialization Juergen Gross
2017-04-18 6:31 ` [PATCH v3 11/11] x86/cpu: remove hypervisor specific set_cpu_features Juergen Gross
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=e60e4d87-8589-f22e-a5d0-a2d4e4b81d1c@suse.com \
--to=jgross@suse.com \
--cc=andrew.cooper3@citrix.com \
--cc=boris.ostrovsky@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=xen-devel@lists.xenproject.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).