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Re: [Qemu-devel] [PATCH] q35/mch: implement extended TSEG sizes


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] q35/mch: implement extended TSEG sizes
Date: Thu, 8 Jun 2017 18:34:49 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0


On 08/06/2017 18:10, Laszlo Ersek wrote:
> When the guest writes value 0xffff to this register, the value that can be
> read back is that of "mch.extended-tseg-mbytes" -- unless it remains
> 0xffff. The guest is required to write 0xffff first (as opposed to a
> read-only register) because PCI config space is generally not cleared on
> QEMU reset, and after S3 resume or reboot, new guest firmware running on
> old QEMU could read a guest OS-injected value from this register.

I guess that's also a reason not to make it readonly (that is, it would
require some firmware code anyway to test for "readonlyness" and
distinguish old machine types from new)?

Thanks,

Paolo



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