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Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested |
Date: |
Wed, 22 Apr 2015 23:51:40 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 |
another point:
On 04/22/15 23:41, Laszlo Ersek wrote:
> On 04/21/15 17:04, Gerd Hoffmann wrote:
>>> - can the guest somehow use this facility to detect, dynamically, the
>>> presence of this feature? (For now I'm thinking about a static build
>>> flag for OVMF that would enable SMM support, but I'm 99% sure Jordan
>>> will object and ask for a dynamic feature detection.)
>>
>> Hmm. I think if we merge all the smm / smram / tseg patches in one go
>> this should work. Without patches reading the ESMRAMC register returns
>> zero. With the patches the three cache-disable bits are hardcoded to
>> '1'. This should work for detecting tseg support.
>>
>> You also have to test for smm support. The current protocol for this is
>> that seabios checks whenever smm is already initialized (see
>> *_apmc_smm_setup() in seabios/src/fw/smm.c) and if so it skips smm
>> initialization. Right now qemu sets the bit on reset when running on
>> kvm, so seabios doesn't try to use smm. On tcg the bit is clear after
>> reset and seabios actually uses smm mode.
>
> I started looking into this. Basically the condition for SMM/SMRAM
> support is:
>
> Q35 && SMRAM support && SMM support (1)
>
> The first subcondition can be checked via the host bridge devid (and
> OVMF already does, for other purposes).
>
> The second one relies on the ESMRAMC, which is in PCI config space.
>
> The third one is messy. It relies on SMI_EN, which is an ioport at
> PMBA+0x30. It requires a configured PMBA.
>
> The problem for OVMF is the following: this condition is too complex /
> too intrusive to evaluate in order to see whether Q35+SMM+SMRAM are
> available.
>
> For that reason, I'd like to ask if it would be possible to introduce a
> new fw_cfg file that would simply communicate the end result of the
> above expression.
There's another problem with basing this decision in OVMF on
SMI_EN.APMC_EN: it is not an idempotent check. At some point the
firmware itself has to set SMI_EN.APMC_EN.
This is probably no issue for SeaBIOS, but in OVMF there's a bunch of
more-or-less independently dispatched modules that depend on condition
(1), and if I set SMI_EN.APMC_EN in some of those modules myself, then
code that ends up running later cannot reuse SMI_EN.APMC_EN for
determining (1). So I'd have to store the original result in some PCD,
but that itself doesn't guarantee ordering either, so it just becomes a
huge mess.
fw_cfg on the other hand is always available, and this fw_cfg file would
never change.
Thanks!
Laszlo
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, (continued)
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Laszlo Ersek, 2015/04/21
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Gerd Hoffmann, 2015/04/21
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Paolo Bonzini, 2015/04/21
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Gerd Hoffmann, 2015/04/21
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Laszlo Ersek, 2015/04/21
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Gerd Hoffmann, 2015/04/22
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Gerd Hoffmann, 2015/04/22
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Laszlo Ersek, 2015/04/22
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Gerd Hoffmann, 2015/04/22
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Laszlo Ersek, 2015/04/22
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested,
Laszlo Ersek <=
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Gerd Hoffmann, 2015/04/23
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Laszlo Ersek, 2015/04/23
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Laszlo Ersek, 2015/04/23
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Gerd Hoffmann, 2015/04/23
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Laszlo Ersek, 2015/04/23
- Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested, Paolo Bonzini, 2015/04/23
[Qemu-devel] [PATCH 6/6] [wip] tseg, part2, not (yet) tested, Gerd Hoffmann, 2015/04/20