On 10/20/21 8:39 AM, Borislav Petkov wrote:
On Wed, Oct 20, 2021 at 08:39:59PM +0800, Tianyu Lan wrote:
Hyper-V runs paravisor in guest VMPL0 which emulates some functions
(e.g, timer, tsc, serial console and so on) via handling VC exception.
GHCB pages are allocated and set up by the paravisor and report to Linux
guest via MSR register.Hyper-V SEV implementation is unenlightened guest
case which doesn't Linux doesn't handle VC and paravisor in the VMPL0
handle it.
Aha, unenlightened.
So why don't you export the original function by doing this (only
partial diff to show intent only):
---
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index f1d513897baf..bfe82f58508f 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -125,7 +125,7 @@ static enum es_result verify_exception_info(struct ghcb *ghcb, struct es_em_ctxt
return ES_VMM_ERROR;
}
-static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
+static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
struct es_em_ctxt *ctxt,
u64 exit_code, u64 exit_info_1,
u64 exit_info_2)
@@ -138,7 +138,14 @@ static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
ghcb_set_sw_exit_info_1(ghcb, exit_info_1);
ghcb_set_sw_exit_info_2(ghcb, exit_info_2);
- sev_es_wr_ghcb_msr(__pa(ghcb));
+ /*
+ * Hyper-V unenlightened guests use a paravisor for communicating and
+ * GHCB pages are being allocated by that paravisor which uses a
+ * different MSR and protocol.
Just to clarify the comment, the paravisor uses the same GHCB MSR and GHCB
protocol, it just can't use __pa() to get the address of the GHCB. So I
expect that the Hyper-V support sets the address properly before calling
this function.
Thanks,
Tom
+ */
+ if (set_ghcb_msr)
+ sev_es_wr_ghcb_msr(__pa(ghcb));
+
VMGEXIT();
return verify_exception_info(ghcb, ctxt);
