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Message-ID: <f6d27366-e083-b362-b44c-eaf4d3365b53@intel.com>
Date: Mon, 28 Nov 2022 11:48:07 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Dexuan Cui <decui@...rosoft.com>,
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Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] x86/hyperv: Support hypercalls for TDX guests
On 11/28/22 11:37, Dexuan Cui wrote:
>> From: Dave Hansen <dave.hansen@...el.com>
...
>> How do we know, for instance, that no hypercall using this interface
>> will *ever* take the 0x0 physical address as an argument?
>
> A 0x0 physical address as an argument still works: the 0 is passed
> to the hypervisor using GHCI. I believe Hyper-V interprets the 0 as
> an error (if the param is needed), and returns an "invalid parameter"
> error code to the guest.
I don't see any data in the public documentation to support the claim
that 0x0 is a special argument for either the input or output GPA
parameters.
This is despite some actual discussion on things like their alignment
requirements[1] and interactions with overlay pages.
So, either you are mistaken about that behavior, or it looks like the
documentation needs updating.
1.
https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/hypercall-interface
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