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Re: [Qemu-devel] [PATCH 07/10] target-s390x: enable fully implemented fa

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH 07/10] target-s390x: enable fully implemented facilities
Date: Tue, 26 May 2015 12:19:41 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/26/2015 11:05 AM, Aurelien Jarno wrote:
On 2015-05-26 10:29, Alexander Graf wrote:

On 26.05.15 08:02, Aurelien Jarno wrote:
On 2015-05-25 23:47, Alexander Graf wrote:

On 25.05.15 23:13, Aurelien Jarno wrote:
On 2015-05-25 23:04, Alexander Graf wrote:

On 25.05.15 23:02, Aurelien Jarno wrote:
On 2015-05-25 22:39, Alexander Graf wrote:

On 25.05.15 01:47, Aurelien Jarno wrote:
Cc: Alexander Graf <address@hidden>
Cc: Richard Henderson <address@hidden>
Signed-off-by: Aurelien Jarno <address@hidden>
Shouldn't this get populated based on the selected -cpu type?
In the long term yes, but given we only implement one CPU type (or
rather none) in TCG mode, we can consider that's already the case.
There are patches coming from IBM to at least add a list of a good
number of s390x cpu types. I'd really like to make use of that and have
actual CPU types selectable.
I guess they are for the KVM mode. Do they provide the corresponding
facilities list? Probably otherwise that doesn't really differentiate
various CPUs. Please make sure of that when reviewing these patches.
I could definitely use help on review - it's probably my weakest point ;).

At least let's move towards that model. So the code in question should
take the facility capabilities from the first cpu object (or the class?)
for example and we bump it to the currently supported feature set in there.
Yes, that would work for STFL/STFLE, though we should have a list of
facilities implemented by TCG so we can mask out the non-implemented
facilities. This basically corresponds to the informations provided by
the current patch.
Ah, so you consider the current list the "these are the features TCG
knows about" list?

That said that won't work for actually disabling the corresponding
instructions as we don't have a 1 to 1 mapping between the facilities
and the group of instructions. Anyway we don't even check that right
I agree, but the TCG code annotates which facility each opcode belongs
to which means actually limiting it should become trivial. That's really
all I'm asking for - I want to see the light at the end of the tunnel ;).
It's trivial doing so for the facilities annotated in TCG. Just that
they don't match one to one with the facilities bits in STFL/STFLE. Some
bits enable multiple facilities and QEMU has also grouped some
facilities together. Also some bits do not actually concern instructions
but rather MMU features. Some other gives additional properties to a
facility: some facilities might be present by disabled, some other might
have a slow or fast implementation.

We therefore need a conversion function before being able to do that,
and we need to know which format IBM is going to provide in their
patches: list of facilities or STFL/STFLE bits?
Please check out this patch set:

Thanks, at a first glance it seems we have what we need. I'll try
to base my STFL/STFLE patches on this patchset in the next days.

Awesome, thanks a lot!


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