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

Sean Christopherson
2020-05-20T06:38:49Z

On Tue, Apr 28, 2020 at 05:17:09PM +0200, Joerg Roedel wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
>
> Implement a handler for #VC exceptions caused by MONITOR and MONITORX
> instructions.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> [ jroedel@suse.de: Adapt to #VC handling infrastructure ]
> Co-developed-by: Joerg Roedel <jroedel@suse.de>
> Signed-off-by: Joerg Roedel <jroedel@suse.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
>