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Re: [Xen-devel] [PATCH 0/6] x86/suspend: State cleanup
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 18 Dec 2019 11:39:49 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 18 Dec 2019 11:40:05 +0000
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On 17/12/2019 16:39, Jan Beulich wrote:
> On 17.12.2019 17:33, Andrew Cooper wrote:
>> On 17/12/2019 16:17, Jan Beulich wrote:
>>> On 13.12.2019 20:04, Andrew Cooper wrote:
>>>> Andrew Cooper (6):
>>>> x86/suspend: Clarify and improve the behaviour of do_suspend_lowlevel()
>>>> x86/suspend: Don't bother saving %cr3, %ss or flags
>>>> x86/suspend: Don't save unnecessary GPRs
>>>> x86/suspend: Restore cr4 later during resume
>>>> x86/suspend: Expand macros in wakeup_prot.S
>>>> x86/suspend: Drop save_rest_processor_state() completely
>>>>
>>>> xen/arch/x86/acpi/suspend.c | 55 ++--------------
>>>> xen/arch/x86/acpi/wakeup_prot.S | 136
>>>> ++++++++++++----------------------------
>>>> xen/arch/x86/boot/wakeup.S | 2 +-
>>>> 3 files changed, 46 insertions(+), 147 deletions(-)
>>> Based on Roger's review
>>> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>
>>> One remark on the combination of patches 2 and 5: The loading of
>>> the stack related registers would now seem to be a fair candidate
>>> for using LSS (generally to be preferred over MOV-to-SS).
>> Well... You've just fixed c/s ffa21ea5303 in the emulator, and it
>> demonstrates why LSS can't be used.
> Hmm, indeed, how did I forget? (It's really very counter-intuitive
> for this insn to not be universally usable.)
The differing behaviour between Intel and AMD makes L*S and call gates
totally unusable, even in situations where they might be useful.
In practice, call gates where killed by SYS{CALL,ENTER}/{RET,EXIT} being
4x faster than anything referencing the IDT/GDT, and L*S have had a
complicated history of availability even in the 32bit days.
~Andrew
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