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

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Date:   Tue, 19 May 2020 23:38:45 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Joerg Roedel <joro@...tes.org>
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, Apr 28, 2020 at 05:17:09PM +0200, Joerg Roedel wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> Implement a handler for #VC exceptions caused by MONITOR and MONITORX
> instructions.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> [ jroedel@...e.de: Adapt to #VC handling infrastructure ]
> Co-developed-by: Joerg Roedel <jroedel@...e.de>
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  arch/x86/kernel/sev-es.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> index 601554e6360f..1a961714cd1b 100644
> --- a/arch/x86/kernel/sev-es.c
> +++ b/arch/x86/kernel/sev-es.c
> @@ -824,6 +824,22 @@ static enum es_result vc_handle_rdpmc(struct ghcb *ghcb, struct es_em_ctxt *ctxt
>  	return ES_OK;
>  }
>  
> +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.

> +}
> +
>  static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
>  					 struct ghcb *ghcb,
>  					 unsigned long exit_code)
> @@ -860,6 +876,9 @@ static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
>  	case SVM_EXIT_WBINVD:
>  		result = vc_handle_wbinvd(ghcb, ctxt);
>  		break;
> +	case SVM_EXIT_MONITOR:
> +		result = vc_handle_monitor(ghcb, ctxt);
> +		break;
>  	case SVM_EXIT_NPF:
>  		result = vc_handle_mmio(ghcb, ctxt);
>  		break;
> -- 
> 2.17.1
>