Re: [PATCH] x86/CPU/AMD: Ignore invalid reset reason value

[Borislav Petkov <bp@alien8.de>]

On Mon, Aug 18, 2025 at 07:24:26AM -0700, Sean Christopherson wrote:
> Most definitely not if the guest owner and host owner are not one and the same.
> The example use case is where the platform owner is running one of _their_ kernels
> in a VM, in which case that kernel probably does want to know why the platform
> reboot.

Except that can you control who uses that feature? If it ends up being used by
a VM stack where the guest owner should not know the reboot reason, you've
lost.

> The same thing that guarantees hardware vendors adhere to specs: the desire to
> get paid.

So you're basically saying all HV vendors return -1 for an unimplemented
register and we should be fine there?

> And QEMU did return an error value, 0xffffffff, a.k.a. PCI Master Abort / PCIe
> Unsupported Request.  I would be amazed if any real world, general purpose VMM
> did anything else for an MMIO access to an unknown/unsupported range.

Ok, I guess we will know soon enough. :-)

> Huh?  Handle a read of all 0xffs as proposed in this patch, and this is unnecessary.

I don't trust that all HVs will DTRT. But ok, I'll take your word for it. We
can run with this and we'll know soon enough whether fishing out -1 is good
enough. And then we'll have more fun.

Thx.

-- 
Regards/Gruss,
    Boris.

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