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Date:   Fri, 20 Mar 2020 23:21:02 +0100
From:   Joerg Roedel <joro@8bytes.org>
To:     David Rientjes <rientjes@google.com>
Cc:     erdemaktas@google.com, x86@kernel.org, hpa@zytor.com,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        Jiri Slaby <jslaby@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Juergen Gross <jgross@suse.com>,
        Kees Cook <keescook@chromium.org>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH 62/70] x86/kvm: Add KVM specific VMMCALL handling under
 SEV-ES
Message-ID: <20200320222102.GM5122@8bytes.org>
References: <20200319091407.1481-1-joro@8bytes.org>
 <20200319091407.1481-63-joro@8bytes.org>
 <alpine.DEB.2.21.2003201423230.205664@chino.kir.corp.google.com>
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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