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Re: [edk2-devel] [Qemu-devel] [PATCH 1/2] q35: implement 128K SMRAM at d
From: |
Laszlo Ersek |
Subject: |
Re: [edk2-devel] [Qemu-devel] [PATCH 1/2] q35: implement 128K SMRAM at default SMBASE address |
Date: |
Mon, 7 Oct 2019 11:44:35 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 |
On 10/04/19 13:31, Igor Mammedov wrote:
> On Tue, 1 Oct 2019 20:03:20 +0200
> "Laszlo Ersek" <address@hidden> wrote:
>> (1) What values to use.
> SeaBIOS writes 0x00 into command port, but it seems that's taken by
> EFI_SMM_COMMUNICATION_PROTOCOL. So we can use the next unused value
> (lets say 0x4). We probably don't have to use status port or
> EFI_SMM_COMMUNICATION_PROTOCOL, since the value of written into 0xB2
> is sufficient to distinguish hotplug event.
Thanks. Can you please write a QEMU patch for the ACPI generator such
that hotplugging a VCPU writes value 4 to IO port 0xB2?
That will allow me to experiment with OVMF.
(I can experiment with some other parts in edk2 even before that.)
>> (2) How the parameters are passed.
>>
>>
>> (2a) For the new CPU, the SMI remains pending, until it gets an
>> INIT-SIPI-SIPI from one of the previously plugged CPUs (most likely, the
>> BSP). At that point, the new CPU will execute the "initial SMI handler
>> for hotplugged CPUs", at the default SMBASE.
>>
>> That's a routine we'll have to write in assembly, from zero. In this
>> routine, we can read back IO ports 0xB2 and 0xB3. And QEMU will be happy
>> to provide the values last written (see apm_ioport_readb() in
>> "hw/isa/apm.c"). So we can receive the values in this routine. Alright.
>
> Potentially we can can avoid writing custom SMI handler,
> what do you think about following workflow:
>
> on system boot after initial CPUs relocation, firmware set NOP SMI handler
> at default SMBASE.
> Then as reaction to GPE triggered SMI (on cpu hotplug), after SMI rendezvous,
> a host cpu reads IO port 0xB2 and does hotplugged CPUs enumeration.
>
> a) assuming we allow hotplug only in case of negotiated SMI broadcast
> host CPU shoots down all in-flight INIT/SIPI/SIPI for hotpugged CPUs
> to avoid race within relocation handler.
How is that "shootdown" possible?
> After that host CPU in loop
>
> b) it prepares/initializes necessary CPU structures for a hotplugged
> CPU if necessary and replaces NOP SMI handler with the relocation
> SMI handler that is used during system boot.
>
> c) a host CPU sends NOP INIT/SIPI/SIPI to the hotplugged CPU
>
> d) the woken up hotplugged CPU, jumps to default SMBASE and
> executes hotplug relocation handler.
>
> e) after the hotplugged CPU is relocated and if there are more
> hotplugged CPUs, a host CPU repeats b-d steps for the next
> hotplugged CPU.
>
> f) after all CPUs are relocated, restore NOP SMI handler at default
> SMBASE.
>
Thanks
Laszlo