From: Juergen Gross <jgross@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
Xen-devel <xen-devel@lists.xen.org>
Cc: Jan Beulich <JBeulich@suse.com>
Subject: Re: [PATCH for-4.11] x86/traps: Improve code generation for set_ist()
Date: Fri, 27 Apr 2018 15:29:05 +0200 [thread overview]
Message-ID: <51914f52-d66f-e876-1503-d8158969510b@suse.com> (raw)
In-Reply-To: <1524834453-22865-1-git-send-email-andrew.cooper3@citrix.com>
On 27/04/18 15:07, Andrew Cooper wrote:
> The IST field in an IDT entry is a 3 bit field, with 5 adjacent reserved bits
> which we always write as zero. By expressing this as a byte field in a union,
> we turn an invocation of enable_each_ist() from
>
> 4b 8b 14 d3 mov (%r11,%r10,8),%rdx
> 48 b8 ff ff ff ff f8 ff ff ff movabs $0xfffffff8ffffffff,%rax
> 48 be 00 00 00 00 01 00 00 00 movabs $0x100000000,%rsi
> 48 8b 8a 80 00 00 00 mov 0x80(%rdx),%rcx
> 48 21 c1 and %rax,%rcx
> 48 09 f1 or %rsi,%rcx
> 48 be 00 00 00 00 02 00 00 00 movabs $0x200000000,%rsi
> 48 89 8a 80 00 00 00 mov %rcx,0x80(%rdx)
> 48 8b 4a 20 mov 0x20(%rdx),%rcx
> 48 21 c1 and %rax,%rcx
> 48 23 82 20 01 00 00 and 0x120(%rdx),%rax
> 48 09 f1 or %rsi,%rcx
> 48 89 4a 20 mov %rcx,0x20(%rdx)
> 48 b9 00 00 00 00 03 00 00 00 movabs $0x300000000,%rcx
> 48 09 c8 or %rcx,%rax
> 48 89 82 20 01 00 00 mov %rax,0x120(%rdx)
>
> into
>
> 4b 8b 04 d3 mov (%r11,%r10,8),%rax
> c6 80 84 00 00 00 01 movb $0x1,0x84(%rax)
> c6 40 24 02 movb $0x2,0x24(%rax)
> c6 80 24 01 00 00 03 movb $0x3,0x124(%rax)
>
> which is far more simple. As the IDT is typically live, this is more
> obviously safe.
>
> The net delta for this change is:
>
> add/remove: 0/0 grow/shrink: 0/7 up/down: 0/-334 (-334)
>
> While making changes here, tidy up the set_ist() declaration. Drop the
> always_inline (I don't recall why I wrote it like that originally) and the ist
> parameter need not be unsigned long (although it will be const-propagated in
> practice).
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
Juergen
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prev parent reply other threads:[~2018-04-27 13:29 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-27 13:07 [PATCH for-4.11] x86/traps: Improve code generation for set_ist() Andrew Cooper
2018-04-27 13:28 ` Jan Beulich
2018-04-27 13:29 ` Juergen Gross [this message]
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