linux-kernel - Re: [PATCH 62/70] x86/kvm: Add KVM specific VMMCALL handling under SEV-ES

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Message-ID: <20200320222102.GM5122@8bytes.org>
Date:   Fri, 20 Mar 2020 23:21:02 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     erdemaktas@...gle.com, x86@...nel.org, 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 62/70] x86/kvm: Add KVM specific VMMCALL handling under
 SEV-ES

On Fri, Mar 20, 2020 at 02:23:58PM -0700, David Rientjes wrote:
> On Thu, 19 Mar 2020, Joerg Roedel wrote:
> > +#if defined(CONFIG_AMD_MEM_ENCRYPT)
> > +static void kvm_sev_es_hcall_prepare(struct ghcb *ghcb, struct pt_regs *regs)
> > +{
> > +	/* RAX and CPL are already in the GHCB */
> > +	ghcb_set_rbx(ghcb, regs->bx);
> > +	ghcb_set_rcx(ghcb, regs->cx);
> > +	ghcb_set_rdx(ghcb, regs->dx);
> > +	ghcb_set_rsi(ghcb, regs->si);
> 
> Is it possible to check the hypercall from RAX and only copy the needed 
> regs or is there a requirement that they must all be copied 
> unconditionally?

No, there is no such requirement. This could be optimized with hypercall
specific knowledge as it is in the KVM code anyway.

Regards,

	Joerg