[PATCH 2/2] KVM: arm64: Use hVHE in pKVM by default on CPUs with VHE support

[Will Deacon]

The early command line parsing treats "kvm-arm.mode=protected" as an
alias for "id_aa64mmfr1.vh=0", forcing the use of nVHE so that the host
kernel runs at EL1 with the pKVM hypervisor at EL2.

With the introduction of hVHE support in ad744e8cb346 ("arm64: Allow
arm64_sw.hvhe on command line"), the hypervisor can run using the EL2+0
translation regime. This is interesting for unusual CPUs that have VH
stuck to 1, but also because it opens the possibility of a hypervisor
"userspace" in the distant future which could be used to isolate vCPU
contexts in the hypervisor (see Marc's talk from KVM Forum 2022 [1]).

Repaint the "kvm-arm.mode=protected" alias to map to "arm64_sw.hvhe=1",
which will use hVHE on CPUs that support it and remain with nVHE
otherwise.

[1] https://www.youtube.com/watch?v=1F_Mf2j9eIo
Signed-off-by: Will Deacon <will at kernel.org>
---
 arch/arm64/kernel/pi/idreg-override.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c
index 39c9253fcf23..c20549e43a77 100644
--- a/arch/arm64/kernel/pi/idreg-override.c
+++ b/arch/arm64/kernel/pi/idreg-override.c
@@ -210,7 +210,7 @@ static const struct {
 	char	feature[FTR_ALIAS_OPTION_LEN];
 } aliases[] __initconst = {
 	{ "kvm_arm.mode=nvhe",		"arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" },
-	{ "kvm_arm.mode=protected",	"id_aa64mmfr1.vh=0" },
+	{ "kvm_arm.mode=protected",	"arm64_sw.hvhe=1" },
 	{ "arm64.nosve",		"id_aa64pfr0.sve=0" },
 	{ "arm64.nosme",		"id_aa64pfr1.sme=0" },
 	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
-- 
2.45.0.rc0.197.gbae5840b3b-goog