Re: [PATCH] x86/sev-es: Expose __sev_es_ghcb_hv_call() to call ghcb hv call out of sev code
From: Borislav Petkov <bp@alien8.de>
Date: 2021-10-20 13:39:46
Also in:
linux-hyperv, lkml, netdev
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
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. + */ + if (set_ghcb_msr) + sev_es_wr_ghcb_msr(__pa(ghcb)); + VMGEXIT(); return verify_exception_info(ghcb, ctxt);
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette