2020-02-11 14:01:25

by Joerg Roedel

Subject: [PATCH 50/62] x86/sev-es: Handle VMMCALL Events

From: Tom Lendacky <[email protected]>

Implement a handler for #VC exceptions caused by VMMCALL instructions.
This patch is only a starting point, VMMCALL emulation under SEV-ES
needs further hypervisor-specific changes to provide additional state.

Signed-off-by: Tom Lendacky <[email protected]>
[ [email protected]: Adapt to #VC handling infrastructure ]
Co-developed-by: Joerg Roedel <[email protected]>
Signed-off-by: Joerg Roedel <[email protected]>
---
arch/x86/kernel/sev-es.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 8f1e84da6fa6..6bd2cae7eb9c 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -341,6 +341,26 @@ static enum es_result handle_mwait(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
return ghcb_hv_call(ghcb, ctxt, SVM_EXIT_MWAIT, 0, 0);
}

+static enum es_result handle_vmmcall(struct ghcb *ghcb,
+ struct es_em_ctxt *ctxt)
+{
+ enum es_result ret;
+
+ ghcb_set_rax(ghcb, ctxt->regs->ax);
+ ghcb_set_cpl(ghcb, user_mode(ctxt->regs) ? 3 : 0);
+
+ ret = ghcb_hv_call(ghcb, ctxt, SVM_EXIT_VMMCALL, 0, 0);
+ if (ret != ES_OK)
+ return ret;
+
+ if (!ghcb_is_valid_rax(ghcb))
+ return ES_VMM_ERROR;
+
+ ctxt->regs->ax = ghcb->save.rax;
+
+ return ES_OK;
+}
+
static enum es_result handle_vc_exception(struct es_em_ctxt *ctxt,
struct ghcb *ghcb,
unsigned long exit_code,
@@ -374,6 +394,9 @@ static enum es_result handle_vc_exception(struct es_em_ctxt *ctxt,
case SVM_EXIT_MSR:
result = handle_msr(ghcb, ctxt);
break;
+ case SVM_EXIT_VMMCALL:
+ result = handle_vmmcall(ghcb, ctxt);
+ break;
case SVM_EXIT_WBINVD:
result = handle_wbinvd(ghcb, ctxt);
break;
--
2.17.1

2020-02-12 00:16:34

by Andy Lutomirski

Subject: Re: [PATCH 50/62] x86/sev-es: Handle VMMCALL Events

> On Feb 11, 2020, at 5:53 AM, Joerg Roedel <[email protected]> wrote:
>
> From: Tom Lendacky <[email protected]>
>
> Implement a handler for #VC exceptions caused by VMMCALL instructions.
> This patch is only a starting point, VMMCALL emulation under SEV-ES
> needs further hypervisor-specific changes to provide additional state.
>

How about we just don’t do VMMCALL if we’re a SEV-ES guest? Otherwise we add thousands of cycles of extra latency for no good reason.

2020-02-12 13:23:20

by Joerg Roedel

Subject: Re: [PATCH 50/62] x86/sev-es: Handle VMMCALL Events

On Tue, Feb 11, 2020 at 04:14:53PM -0800, Andy Lutomirski wrote:
>
> How about we just don’t do VMMCALL if we’re a SEV-ES guest? Otherwise
> we add thousands of cycles of extra latency for no good reason.

True, but I left that as a future optimization for now, given the size
the patch-set already has. The idea is to add an abstraction around
VMMCALL for the support code of the various hypervisors and just do a
VMGEXIT in that wrapper when in an SEV-ES guest. But again, that is a
separate patch-set.

Regards,

Joerg