linux-kernel - Re: [PATCH 41/62] x86/sev-es: Handle MSR events

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Message-ID: <b688b4ad-5a64-d2df-6dd8-e23fac75a6b9@intel.com>
Date:   Thu, 13 Feb 2020 07:45:00 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Joerg Roedel <joro@...tes.org>, x86@...nel.org
Cc:     hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 41/62] x86/sev-es: Handle MSR events

On 2/11/20 5:52 AM, Joerg Roedel wrote:
> Implement a handler for #VC exceptions caused by RDMSR/WRMSR
> instructions.

As a general comment on all of these event handlers: Why do we bother
having the hypercalls in the interrupt handler as opposed to just
calling them directly.  What you have is:

	wrmsr()
	-> #VC exception
	   hcall()

But we could make our rd/wrmsr() wrappers just do:

	if (running_on_sev_es())
		hcall(HCALL_MSR_WHATEVER...)
	else
		wrmsr()

and then we don't have any of the nastiness of exception handling.