This is a combination of the RFC for nVHE here [1] and v3 of VHE version here [2]. After a few of the review comments it seemed much simpler for both versions to use the same interface and be in the same patchset.
FEAT_TRF is a Coresight feature that allows trace capture to be completely filtered at different exception levels, unlike the existing TRCVICTLR controls which may still emit target addresses of branches, even if the following trace is filtered.
Without FEAT_TRF, it was possible to start a trace session on a host and also collect trace from the guest as TRCVICTLR was never programmed to exclude guests (and it could still emit target addresses even if it was).
With FEAT_TRF, the current behavior of trace in guests exists depends on whether nVHE or VHE are being used. Both of the examples below are from the host's point of view, as Coresight isn't accessible from guests. This patchset is only relevant to when FEAT_TRF exists, otherwise there is no change.
nVHE:
Because the host and the guest are both using TRFCR_EL1, trace will be generated in guests depending on the same filter rules the host is using. For example if the host is tracing userspace only, then guest userspace trace will also be collected.
(This is further limited by whether TRBE is used because an issue with TRBE means that it's completely disabled in nVHE guests, but it's possible to have other tracing components.)
VHE:
With VHE, the host filters will be in TRFCR_EL2, but the filters in TRFCR_EL1 will be active when the guest is running. Because we don't write to TRFCR_EL1, guest trace will be completely disabled.
With this change, the guest filtering rules from the Perf session are honored for both nVHE and VHE modes. This is done by either writing to TRFCR_EL12 at the start of the Perf session and doing nothing else further, or caching the guest value and writing it at guest switch for nVHE.
The first commit moves the register to sysreg because I add the EL12 version in a later commit.
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Changes since nVHE RFC [1]:
* Re-write just in terms of the register value to be written for the host and the guest. This removes some logic from the hyp code and a value of kvm_vcpu_arch:trfcr_el1 = 0 no longer means "don't restore". * Remove all the conditional compilation and new files. * Change the kvm_etm_update_vcpu_events macro to a function. * Re-use DEBUG_STATE_SAVE_TRFCR so iflags don't need to be expanded anymore. * Expand the cover letter.
Changes since VHE v3 [2]:
* Use the same interface as nVHE mode so TRFCR_EL12 is now written by kvm.
[1]: https://lore.kernel.org/kvmarm/20230804101317.460697-1-james.clark@arm.com/ [2]: https://lore.kernel.org/kvmarm/20230905102117.2011094-1-james.clark@arm.com/
James Clark (5): arm64/sysreg: Move TRFCR definitions to sysreg arm64: KVM: Rename DEBUG_STATE_SAVE_TRBE to DEBUG_STATE_SAVE_TRFCR arm64: KVM: Add interface to set guest value for TRFCR register arm64: KVM: Write TRFCR value on guest switch with nVHE coresight: Pass guest TRFCR value to KVM
arch/arm64/include/asm/kvm_host.h | 10 +++- arch/arm64/include/asm/sysreg.h | 12 ---- arch/arm64/kvm/arm.c | 1 + arch/arm64/kvm/debug.c | 38 +++++++++++- arch/arm64/kvm/hyp/nvhe/debug-sr.c | 60 +++++++++++-------- arch/arm64/tools/sysreg | 41 +++++++++++++ .../coresight/coresight-etm4x-core.c | 42 +++++++++++-- drivers/hwtracing/coresight/coresight-etm4x.h | 2 +- drivers/hwtracing/coresight/coresight-priv.h | 3 + 9 files changed, 160 insertions(+), 49 deletions(-)