Re: [Xen-devel] [PATCH] xen,x86: introduce tcg_errata

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 25/01/18 19:43, Stefano Stabellini wrote:
> On Thu, 25 Jan 2018, Andrew Cooper wrote:
>> On 25/01/18 18:37, Stefano Stabellini wrote:
>>> The TCG emulator in QEMU is not good enough to pass the the tests in
>>> stub_selftest. Detect if Xen is running on TCG early, then drop the
>>> tests if it is the case.
>>>
>>> Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>> I'm still opposed to this change.  The selftests demonstrate that TCG
>> doesn't work for an architectural area we depend, and simply pretending
>> its not buggy isn't ok.  If this were a piece of real hardware, it would
>> be blacklisted in a similar fashion to XSA-9.
>> I still haven't seen a convincing enough usecase to cause Xen to
>> proactively look for Qemu in all cases including release builds on real
>> hardware.
> Testing is a very good use case.

Testing is good. I approve of testing.

The problem is that what you are doing here is using a broken testing
tool and instead of fixing the tool, you're bodging Xen to pro-actively
search for your broken testing tool in all cases including release
builds, and ignore one of Xen's safety checks.

This is why I'm unconvinced by the argument.

~Andrew

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