KVM: arm64: Restore missing ISB on nVHE __tlb_switch_to_guest

Marc Zyngier · Marc Zyngier · commit 452d62227958 · 2020-10-01T09:53:45.000+01:00
Commit a0e50aa ("KVM: arm64: Factor out stage 2 page table data from struct kvm") dropped the ISB after __load_guest_stage2(), only leaving the one that is required when the speculative AT workaround is in effect. As Andrew points it: "This alternative is 'backwards' to avoid a double ISB as there is one in __load_guest_stage2 when the workaround is active." Restore the missing ISB, conditionned on the AT workaround not being active. Fixes: a0e50aa ("KVM: arm64: Factor out stage 2 page table data from struct kvm") Reported-by: Andrew Scull <ascull@google.com> Reported-by: Thomas Tai <thomas.tai@oracle.com> Signed-off-by: Marc Zyngier <maz@kernel.org>
diff --git a/arch/arm64/kvm/hyp/nvhe/tlb.c b/arch/arm64/kvm/hyp/nvhe/tlb.c
@@ -31,7 +31,14 @@ static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
 		isb();
 	}
 
+	/*
+	 * __load_guest_stage2() includes an ISB only when the AT
+	 * workaround is applied. Take care of the opposite condition,
+	 * ensuring that we always have an ISB, but not two ISBs back
+	 * to back.
+	 */
 	__load_guest_stage2(mmu);
+	asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));
 }
 
 static void __tlb_switch_to_host(struct tlb_inv_context *cxt)

Original file line number	Diff line number	Diff line change
`@@ -31,7 +31,14 @@ static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,`
`31`	`31`	`isb();`
`32`	`32`	`}`
`33`	`33`
	`34`	`+ /*`
	`35`	`+ * __load_guest_stage2() includes an ISB only when the AT`
	`36`	`+ * workaround is applied. Take care of the opposite condition,`
	`37`	`+ * ensuring that we always have an ISB, but not two ISBs back`
	`38`	`+ * to back.`
	`39`	`+ */`
`34`	`40`	`__load_guest_stage2(mmu);`
	`41`	`+ asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));`
`35`	`42`	`}`
`36`	`43`
`37`	`44`	`static void __tlb_switch_to_host(struct tlb_inv_context *cxt)`