On Fri, 04 Aug 2023 11:13:12 +0100,
James Clark james.clark@arm.com wrote:
Currently trace will always be generated in nVHE as long as TRBE isn't
being used. To allow filtering out guest trace, re-apply the filter
rules before switching to the guest.
The TRFCR restore function remains the same.
arch/arm64/kvm/debug.c | 7 ++++
arch/arm64/kvm/hyp/nvhe/debug-sr.c | 56 +++++++++++++++++++++++++++---
2 files changed, 59 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 8725291cb00a..ebb4db20a859 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -335,10 +335,17 @@ void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceBuffer_SHIFT) &&
!(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
- /*
* Save TRFCR on nVHE if FEAT_TRF exists. This will be done in cases
* where DEBUG_STATE_SAVE_TRBE doesn't completely disable trace.
*/
- if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceFilt_SHIFT))
vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRFCR);
}
void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
{
vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE);
vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
- vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRFCR);
}
diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
index 4558c02eb352..0e8c85b29b92 100644
--- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
+++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
@@ -51,13 +51,17 @@ static void __debug_restore_spe(u64 pmscr_el1)
write_sysreg_s(pmscr_el1, SYS_PMSCR_EL1);
}
-static void __debug_save_trace(u64 *trfcr_el1)
+/*
- Save TRFCR and disable trace completely if TRBE is being used. Return true
-
- */
+static bool __debug_save_trace(u64 *trfcr_el1)
{
*trfcr_el1 = 0;
/* Check if the TRBE is enabled */
if (!(read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_EL1_E))
While you're refactoring this code, please move the zeroing of
*trfcr_el1 under the if statement.
/*
* Prohibit trace generation while we are in guest.
* Since access to TRFCR_EL1 is trapped, the guest can't
@@ -68,6 +72,8 @@ static void __debug_save_trace(u64 *trfcr_el1)
isb();
/* Drain the trace buffer to memory */
tsb_csync();
}
static void __debug_restore_trace(u64 trfcr_el1)
@@ -79,14 +85,55 @@ static void __debug_restore_trace(u64 trfcr_el1)
write_sysreg_s(trfcr_el1, SYS_TRFCR_EL1);
}
+#if IS_ENABLED(CONFIG_PERF_EVENTS)
As previously stated, just always compile this. There shouldn't be
anything here that's so large that it becomes a candidate for
exclusion. Hell, even the whole of NV+pKVM are permanent features,
even of most people won't use *any* of that.
+static inline void __debug_save_trfcr(struct kvm_vcpu *vcpu)
+{
I find this "zero means do nothing" part very odd. I can see it is
already done, but I really dislike this sort of assumption to avoid
writing to a register.
I'd really prefer we track another version of TRFCR_EL1, compare host
and guest, and decide to avoid writing if they are equal. At least, it
would be readable.
And in the end, expressing *everything* in terms of the register would
really help, instead of the exclude_* stuff that has no place in the
low-level arch code.
Yep, I agree with all of the above, I can make these changes for the
next version. I just want to clarify your point about disabling trace
for protected guests when not in debug mode that I asked about in the
review on patch 1.