Hi Julien,
On Tue, Nov 14, 2017 at 04:42:13PM +0000, Julien Thierry wrote:
> 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' ?
Yes.
>
> 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)
spi ?
> - save spe -> returns early without setting pmscr_el1
> - restore spe with old save instead of doing nothing
>
I think I see what you mean. Basically you're asking if we need this:
diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
index 4112160..8ab3510 100644
--- a/arch/arm64/kvm/hyp/debug-sr.c
+++ b/arch/arm64/kvm/hyp/debug-sr.c
@@ -106,7 +106,7 @@ static void __hyp_text __debug_save_spe_nvhe(u64 *pmscr_el1)
static void __hyp_text __debug_restore_spe_nvhe(u64 &pmscr_el1)
{
- if (!pmscr_el1)
+ if (*pmscr_el1 != 0)
return;
/* The host page table is installed, but not yet synchronised */
@@ -114,6 +114,7 @@ static void __hyp_text __debug_restore_spe_nvhe(u64 &pmscr_el1)
/* Re-enable data generation */
write_sysreg_s(pmscr_el1, PMSCR_EL1);
+ *pmscr_el1 = 0;
}
void __hyp_text __debug_save_state(struct kvm_vcpu *vcpu,
I think we do, and I think this is a separate fix. Would you like to
write a patch and cc Will and Marc (original author and committer) to
fix this? Probably worth a cc stable as well.
Thanks,
-Christoffer
