linux-kernel - Re: [PATCH v3 59/75] x86/sev-es: Handle MONITOR/MONITORX Events

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Message-ID: <20200611131045.GE11924@8bytes.org>
Date:   Thu, 11 Jun 2020 15:10:45 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     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>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 59/75] x86/sev-es: Handle MONITOR/MONITORX Events

On Tue, May 19, 2020 at 11:38:45PM -0700, Sean Christopherson wrote:
> On Tue, Apr 28, 2020 at 05:17:09PM +0200, Joerg Roedel wrote:
> > +static enum es_result vc_handle_monitor(struct ghcb *ghcb,
> > +					struct es_em_ctxt *ctxt)
> > +{
> > +	phys_addr_t monitor_pa;
> > +	pgd_t *pgd;
> > +
> > +	pgd = __va(read_cr3_pa());
> > +	monitor_pa = vc_slow_virt_to_phys(ghcb, ctxt->regs->ax);
> > +
> > +	ghcb_set_rax(ghcb, monitor_pa);
> > +	ghcb_set_rcx(ghcb, ctxt->regs->cx);
> > +	ghcb_set_rdx(ghcb, ctxt->regs->dx);
> > +
> > +	return sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_MONITOR, 0, 0);
> 
> Why?  If SVM has the same behavior as VMX, the MONITOR will be disarmed on
> VM-Enter, i.e. the VMM can't do anything useful for MONITOR/MWAIT.  I
> assume that's the case given that KVM emulates MONITOR/MWAIT as NOPs on
> SVM.

Not sure if it is disarmed on VMRUN, but the MONITOR/MWAIT instructions
are part of the GHCB spec, so they are implemented here.


	Joerg