[PATCH] KVM: arm64: Fixes ARM VM hangs at boot

[Thomas Tai]

When using the latest kernel v5.9-rc7 on an ARM server, VMs could
hang at boot with no output. The commit a0e50aa3f4a8 removed
asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT)),
it looks like isb is still needed for non
ARM64_WORKAROUND_SPECULATIVE_AT host when switching to guest.

The code fragment for the original patch:
-       /* __load_guest_stage2() includes an ISB for the workaround. */
-       __load_guest_stage2(kvm);
-       asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));
+       __load_guest_stage2(mmu);

The code should have been:
-       /* __load_guest_stage2() includes an ISB for the workaround. */
-       __load_guest_stage2(kvm);
-       asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));
+       __load_guest_stage2(mmu);
+       asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));
ie, the workaround is still needed.

Fixes: a0e50aa3f4a8 ("KVM: arm64: Factor out stage 2 page table data from
struct kvm")

Signed-off-by: Thomas Tai <thomas.tai at oracle.com>
---
 arch/arm64/kvm/hyp/nvhe/tlb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/tlb.c b/arch/arm64/kvm/hyp/nvhe/tlb.c
index 69eae60..536496e 100644
--- a/arch/arm64/kvm/hyp/nvhe/tlb.c
+++ b/arch/arm64/kvm/hyp/nvhe/tlb.c
@@ -32,6 +32,7 @@ static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
 	}
 
 	__load_guest_stage2(mmu);
+	asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));
 }
 
 static void __tlb_switch_to_host(struct tlb_inv_context *cxt)
-- 
1.8.3.1