Hi Christopher,
On 12/10/17 11:41, Christoffer Dall wrote:
The debug save/restore functions can be improved by using the has_vhe()
static key instead of the instruction alternative. Using the static key
uses the same paradigm as we're going to use elsewhere, it makes the
code more readable, and it generates slightly better code (no
stack setups and function calls unless necessary).
We also use a static key on the restore path, because it will be
marginally faster than loading a value from memory.
Finally, we don't have to conditionally clear the debug dirty flag if
it's set, we can just clear it.
Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
---
arch/arm64/kvm/hyp/debug-sr.c | 22 +++++++++-------------
1 file changed, 9 insertions(+), 13 deletions(-)
diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
index 0fc0758..a2291b6 100644
--- a/arch/arm64/kvm/hyp/debug-sr.c
+++ b/arch/arm64/kvm/hyp/debug-sr.c
@@ -75,11 +75,6 @@
#define psb_csync() asm volatile("hint #17")
-static void __hyp_text __debug_save_spe_vhe(u64 *pmscr_el1)
-{
- /* The vcpu can run. but it can't hide. */
-}
-
static void __hyp_text __debug_save_spe_nvhe(u64 *pmscr_el1)
{
u64 reg;
@@ -109,10 +104,6 @@ static void __hyp_text __debug_save_spe_nvhe(u64 *pmscr_el1)
dsb(nsh);
}
-static hyp_alternate_select(__debug_save_spe,
- __debug_save_spe_nvhe, __debug_save_spe_vhe,
- ARM64_HAS_VIRT_HOST_EXTN);
-
static void __hyp_text __debug_restore_spe(u64 pmscr_el1)
{
if (!pmscr_el1)
@@ -174,17 +165,22 @@ void __hyp_text __debug_cond_save_host_state(struct kvm_vcpu *vcpu)
{
__debug_save_state(vcpu, &vcpu->arch.host_debug_state.regs,
kern_hyp_va(vcpu->arch.host_cpu_context));
- __debug_save_spe()(&vcpu->arch.host_debug_state.pmscr_el1);
+
+ /* Non-VHE: Disable and flush SPE data generation
+ * VHE: The vcpu can run. but it can't hide. */
+ if (!has_vhe())
+ __debug_save_spe_nvhe(&vcpu->arch.host_debug_state.pmscr_el1);
}
void __hyp_text __debug_cond_restore_host_state(struct kvm_vcpu *vcpu)
{
- __debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
+ if (!has_vhe())
+ __debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
For consistency, would it be worth naming that function
'__debug_restore_spe_nvhe' ?
Also, looking at __debug_save_spe_nvhe, I'm not sure how we guarantee
that we might not end up using stale data during the restore_spe
(though, if this is an issue, it existed before this change).
The save function might exit without setting a value to saved pmscr_el1.
Basically I'm wondering if the following scenario (in non VHE) is
possible and/or whether it is problematic:
- save spe
- restore spe
- host starts using spi -> !(PMBLIMITR_EL1 & PMBLIMITR_EL1_E)
- save spe -> returns early without setting pmscr_el1
- restore spe with old save instead of doing nothing
Cheers,
--
Julien Thierry
