Re: [Xen-devel] [PATCH v2 6/6] x86/boot: Do not use trampoline for no-real-mode boot paths

["David Woodhouse" <dwmw2@xxxxxxxxxxxxx>]

> On 19.08.2019 17:25, David Woodhouse wrote:
>> On Mon, 2019-08-12 at 12:55 +0200, Jan Beulich wrote:
>>> On 09.08.2019 17:02, David Woodhouse wrote:
>>>> @@ -97,7 +100,7 @@ GLOBAL(trampoline_realmode_entry)
>>>>           cld
>>>>           cli
>>>>           lidt    trampsym(idt_48)
>>>> -        lgdt    trampsym(gdt_48)
>>>> +        lgdtl   trampsym(gdt_48)
>>>
>>> Stray / unrelated change (and if needed, then also for lidt)?
>>
>> The difference between 16bit l.dt and 32-bit l.dtl is that the former
>> only loads 24 bits of the actual table address (trampoline_gdt in this
>> case).
>>
>> Thus, when trampoline_gdt is being used in-place, as it is during early
>> boot, and *if* the Xen image is loaded higher than 16MiB, lgdt doesn't
>> work. That's half a day of my life I want back.
>
> But isn't this an issue even independent of your series? I.e. doesn't
> this want to be fixed in a separate (to be backported) patch?

Before my series it isn't used in place in the Xen image; it's also
(mostly gratuitously) copied to low memory.

-- 
dwmw2


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