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Message-ID: <1d2a6c09-6892-48fc-a7fb-e171c7fbd814@arm.com>
Date: Mon, 26 Feb 2024 10:14:56 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: James Clark <james.clark@....com>, coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
maz@...nel.org, acme@...nel.org, oliver.upton@...ux.dev, broonie@...nel.org
Cc: James Morse <james.morse@....com>, Zenghui Yu <yuzenghui@...wei.com>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
Mike Leach <mike.leach@...aro.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Anshuman Khandual <anshuman.khandual@....com>,
Miguel Luis <miguel.luis@...cle.com>, Joey Gouly <joey.gouly@....com>,
Ard Biesheuvel <ardb@...nel.org>, Arnd Bergmann <arnd@...db.de>,
Helge Deller <deller@....de>, Greg Kroah-Hartman
<gregkh@...uxfoundation.org>, Mark Rutland <mark.rutland@....com>,
Kalesh Singh <kaleshsingh@...gle.com>, Ryan Roberts <ryan.roberts@....com>,
Vincent Donnefort <vdonnefort@...gle.com>, Fuad Tabba <tabba@...gle.com>,
Jing Zhang <jingzhangos@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 6/7] arm64: KVM: Write TRFCR value on guest switch with
nVHE
On 20/02/2024 10:09, James Clark wrote:
> The guest value for TRFCR requested by the Coresight driver is saved in
> kvm_guest_trfcr. On guest switch this value needs to be written to
> the register. Currently TRFCR is only modified when we want to disable
> trace completely in guests due to an issue with TRBE. Expand the
> __debug_save_trace() function to always write to the register if a
> different value for guests is required, but also keep the existing TRBE
> disable behavior if that's required.
>
> In pKVM, the kvm_guest_trfcr can't be read and the host isn't trusted,
> so always disable trace.
>
> __debug_restore_trace() now has to restore unconditionally, because even
> a value of 0 needs to be written to overwrite whatever was set for the
> guest.
>
> Signed-off-by: James Clark <james.clark@....com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
> arch/arm64/kvm/hyp/nvhe/debug-sr.c | 53 +++++++++++++++++-------------
> 1 file changed, 31 insertions(+), 22 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> index 4558c02eb352..3adac2e01908 100644
> --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> @@ -51,30 +51,39 @@ static void __debug_restore_spe(u64 pmscr_el1)
> write_sysreg_s(pmscr_el1, SYS_PMSCR_EL1);
> }
>
> -static void __debug_save_trace(u64 *trfcr_el1)
> +static void __debug_save_trace(struct kvm_vcpu *vcpu)
> {
> - *trfcr_el1 = 0;
> -
> - /* Check if the TRBE is enabled */
> - if (!(read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_EL1_E))
> - return;
> - /*
> - * Prohibit trace generation while we are in guest.
> - * Since access to TRFCR_EL1 is trapped, the guest can't
> - * modify the filtering set by the host.
> - */
> - *trfcr_el1 = read_sysreg_s(SYS_TRFCR_EL1);
> - write_sysreg_s(0, SYS_TRFCR_EL1);
> - isb();
> - /* Drain the trace buffer to memory */
> - tsb_csync();
> + u64 host_trfcr_el1 = read_sysreg_s(SYS_TRFCR_EL1);
> + u64 guest_trfcr_el1;
> +
> + vcpu->arch.host_debug_state.trfcr_el1 = host_trfcr_el1;
> +
> + /* Check if the TRBE buffer or pKVM is enabled */
> + if (is_protected_kvm_enabled() ||
> + (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRBE) &&
> + read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_EL1_E)) {
> + /*
> + * Prohibit trace generation while we are in guest. Since access
> + * to TRFCR_EL1 is trapped, the guest can't modify the filtering
> + * set by the host.
> + */
> + write_sysreg_s(0, SYS_TRFCR_EL1);
> + isb();
> + /* Drain the trace buffer to memory */
> + tsb_csync();
> + } else {
> + /*
> + * Tracing is allowed, apply the filters provided by the
> + * Coresight driver.
> + */
> + guest_trfcr_el1 = kvm_guest_trfcr[vcpu->cpu];
> + if (host_trfcr_el1 != guest_trfcr_el1)
> + write_sysreg_s(guest_trfcr_el1, SYS_TRFCR_EL1);
> + }
> }
>
> static void __debug_restore_trace(u64 trfcr_el1)
> {
> - if (!trfcr_el1)
> - return;
> -
> /* Restore trace filter controls */
> write_sysreg_s(trfcr_el1, SYS_TRFCR_EL1);
> }
> @@ -85,8 +94,8 @@ void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
> if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_SPE))
> __debug_save_spe(&vcpu->arch.host_debug_state.pmscr_el1);
> /* Disable and flush Self-Hosted Trace generation */
> - if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRBE))
> - __debug_save_trace(&vcpu->arch.host_debug_state.trfcr_el1);
> + if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRFCR))
> + __debug_save_trace(vcpu);
> }
>
> void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
> @@ -98,7 +107,7 @@ void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu)
> {
> if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_SPE))
> __debug_restore_spe(vcpu->arch.host_debug_state.pmscr_el1);
> - if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRBE))
> + if (vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRFCR))
> __debug_restore_trace(vcpu->arch.host_debug_state.trfcr_el1);
> }
>
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