[PATCH] arm64: KVM: Guests can skip __install_bp_hardening_cb()s HYP work

[PATCH] arm64: KVM: Guests can skip __install_bp_hardening_cb()s HYP work

[James Morse]

enable_smccc_arch_workaround_1() passes NULL as the hyp_vecs start and
end if the HVC conduit is in use, and ARM_SMCCC_ARCH_WORKAROUND_1 is
detected.

If the guest kernel happened to be built with KVM_INDIRECT_VECTORS,
we go on to allocate a slot, memcpy() the empty workaround in and
do the appropriate cache maintenance.

This works as we always tell memcpy() the range is 0, so it never
accesses the NULL src pointer, but we still do the cache maintenance.

If hyp_vecs_start is NULL we know we're a guest, just update the fn
like the !KVM_INDIRECT_VECTORS version.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
---
 arch/arm64/kernel/cpu_errata.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index dec10898d688..25305f8a8670 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -116,6 +116,15 @@ static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
 	static DEFINE_SPINLOCK(bp_lock);
 	int cpu, slot = -1;
 
+	/*
+	 * enable_smccc_arch_workaround_1() passes NULL for the hyp_vecs
+	 * start/end if we're a guest. Skip the hyp-vectors work.
+	 */
+	if (!hyp_vecs_start) {
+		__this_cpu_write(bp_hardening_data.fn, fn);
+		return;
+	}
+
 	spin_lock(&bp_lock);
 	for_each_possible_cpu(cpu) {
 		if (per_cpu(bp_hardening_data.fn, cpu) == fn) {
-- 
2.18.0

[PATCH] arm64: KVM: Guests can skip __install_bp_hardening_cb()s HYP work

[Marc Zyngier]

On 21/09/18 21:49, James Morse wrote:
> enable_smccc_arch_workaround_1() passes NULL as the hyp_vecs start and
> end if the HVC conduit is in use, and ARM_SMCCC_ARCH_WORKAROUND_1 is
> detected.
> 
> If the guest kernel happened to be built with KVM_INDIRECT_VECTORS,
> we go on to allocate a slot, memcpy() the empty workaround in and
> do the appropriate cache maintenance.
> 
> This works as we always tell memcpy() the range is 0, so it never
> accesses the NULL src pointer, but we still do the cache maintenance.
> 
> If hyp_vecs_start is NULL we know we're a guest, just update the fn
> like the !KVM_INDIRECT_VECTORS version.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> Reviewed-by: Julien Thierry <julien.thierry@arm.com>

Acked-by: Marc Zyngier <marc.zyngier@arm.com>

Catalin: could you sneak this one in for 4.20? It is strictly a KVM
patch, but its location makes it more suitable for the arm64 tree...

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

[PATCH] arm64: KVM: Guests can skip __install_bp_hardening_cb()s HYP work

[Catalin Marinas]

On Fri, Oct 19, 2018 at 11:17:32AM +0100, Marc Zyngier wrote:
> On 21/09/18 21:49, James Morse wrote:
> > enable_smccc_arch_workaround_1() passes NULL as the hyp_vecs start and
> > end if the HVC conduit is in use, and ARM_SMCCC_ARCH_WORKAROUND_1 is
> > detected.
> > 
> > If the guest kernel happened to be built with KVM_INDIRECT_VECTORS,
> > we go on to allocate a slot, memcpy() the empty workaround in and
> > do the appropriate cache maintenance.
> > 
> > This works as we always tell memcpy() the range is 0, so it never
> > accesses the NULL src pointer, but we still do the cache maintenance.
> > 
> > If hyp_vecs_start is NULL we know we're a guest, just update the fn
> > like the !KVM_INDIRECT_VECTORS version.
> > 
> > Signed-off-by: James Morse <james.morse@arm.com>
> > Reviewed-by: Julien Thierry <julien.thierry@arm.com>
> 
> Acked-by: Marc Zyngier <marc.zyngier@arm.com>
> 
> Catalin: could you sneak this one in for 4.20? It is strictly a KVM
> patch, but its location makes it more suitable for the arm64 tree...

Done.

-- 
Catalin