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From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH v2 5/7] x86/traps: Lift all non-entrypoint logic in entry_int82() up into C
Date: Thu, 04 May 2017 04:28:29 -0600	[thread overview]
Message-ID: <590B1E6D0200007800156BBC@prv-mh.provo.novell.com> (raw)
In-Reply-To: <abda0c8f-0241-a328-1872-54e187b4ad4e@citrix.com>

>>> On 04.05.17 at 12:16, <andrew.cooper3@citrix.com> wrote:
> On 04/05/17 11:01, Andrew Cooper wrote:
> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -21,6 +21,7 @@ ENTRY(entry_int82)
>  
>          mov   %rsp, %rdi
>          call  do_entry_int82
> +        jmp   compat_test_all_events
>  
>  /* %rbx: struct vcpu */
>  ENTRY(compat_test_all_events)
> 
> 
> This only currently works because the ALIGN hidden in ENTRY() happens to
> be safe to execute through, but we shouldn't rely on this,

Why not? ALIGN is the way it is for a reason.

> and a single predicted jump is probably faster to execute than
> a line of single-byte nops.

I'm not sure about this, but it's possible. A question is whether we
really should force 0x90 fillers in ALIGN, rather than having the
assembler use multi-bytes NOPs when suitable.

Jan


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  reply	other threads:[~2017-05-04 10:28 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-02 18:05 [PATCH 0/7] XSAs 213-315 followups Andrew Cooper
2017-05-02 18:05 ` [PATCH 1/7] x86/traps: Drop 32bit fields out of tss_struct Andrew Cooper
2017-05-03  8:10   ` Jan Beulich
2017-05-03 12:33     ` Andrew Cooper
2017-05-03  9:48   ` Wei Liu
2017-05-02 18:05 ` [PATCH 2/7] x86/traps: Poison unused stack pointers in the TSS Andrew Cooper
2017-05-03  8:14   ` Jan Beulich
2017-05-03 12:47     ` Andrew Cooper
2017-05-03 13:29   ` [PATCH v2 " Andrew Cooper
2017-05-03 13:45     ` Jan Beulich
2017-05-02 18:05 ` [PATCH 3/7] x86/mm: Further restrict permissions on some virtual mappings Andrew Cooper
2017-05-03  8:49   ` Jan Beulich
2017-05-03 13:38     ` Andrew Cooper
2017-05-03 13:48       ` Jan Beulich
2017-05-03  9:48   ` Wei Liu
2017-05-03 10:11   ` Tim Deegan
2017-05-03 11:13   ` George Dunlap
2017-05-02 18:05 ` [PATCH 4/7] x86/traps: Rename compat_hypercall() to entry_int82() Andrew Cooper
2017-05-03  8:55   ` Jan Beulich
2017-05-03 13:41     ` Andrew Cooper
2017-05-02 18:05 ` [PATCH 5/7] x86/traps: Lift all non-entrypoint logic in entry_int82() up into C Andrew Cooper
2017-05-03  9:02   ` Jan Beulich
2017-05-03 11:26     ` Wei Liu
2017-05-03 11:38       ` Andrew Cooper
2017-05-03 11:43         ` Wei Liu
2017-05-03 12:02         ` Jan Beulich
2017-05-03 12:18           ` Andrew Cooper
2017-05-03 12:37             ` Jan Beulich
2017-05-03 18:29               ` Andrew Cooper
2017-05-04  7:27                 ` Jan Beulich
2017-05-04  9:27                   ` Andrew Cooper
2017-05-04  9:36                     ` Jan Beulich
2017-05-04  9:57                       ` Andrew Cooper
2017-05-03 12:00       ` Jan Beulich
2017-05-04 10:01     ` [PATCH v2 " Andrew Cooper
2017-05-04 10:16       ` Andrew Cooper
2017-05-04 10:28         ` Jan Beulich [this message]
2017-05-04 11:09           ` Andrew Cooper
2017-05-04 10:22       ` Jan Beulich
2017-05-02 18:05 ` [PATCH 6/7] x86/asm: Fold LOAD_C_CLOBBERED into RESTORE_ALL Andrew Cooper
2017-05-03  9:08   ` Jan Beulich
2017-05-03  9:48   ` Wei Liu
2017-05-02 18:05 ` [PATCH 7/7] x86/asm: Clobber %r{8..15} on exit to 32bit PV guests Andrew Cooper
2017-05-03  9:13   ` Jan Beulich
2017-05-03 17:51     ` [PATCH v2 " Andrew Cooper
2017-05-04  8:50       ` Jan Beulich
2017-05-04 11:11 ` [RFC for 4.9] [PATCH 0/7] XSAs 213-315 followups Andrew Cooper
2017-05-04 12:52   ` Julien Grall

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