Re: [PATCH v5 07/18] kvm: arm64: Configure VTCR_EL2 per VM

From: Suzuki K Poulose
Date: Thu Sep 20 2018 - 06:39:03 EST

Hi Eric,

On 20/09/18 11:21, Auger Eric wrote:
Hi Suzuki,

On 9/17/18 12:41 PM, Suzuki K Poulose wrote:
Add support for setting the VTCR_EL2 per VM, rather than hard
coding a value at boot time per CPU. This would allow us to tune
the stage2 page table parameters per VM in the later changes.

We compute the VTCR fields based on the system wide sanitised
feature registers, except for the hardware management of Access
Flags (VTCR_EL2.HA). It is fine to run a system with a mix of
CPUs that may or may not update the page table Access Flags.
Since the bit is RES0 on CPUs that don't support it, the bit
should be ignored on them.

Suggested-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Acked-by: Christoffer Dall <cdall@xxxxxxxxxx>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index b0c07dab5cb3..e0c49377b771 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -26,6 +26,7 @@

#include <kvm/arm_arch_timer.h>

+#include <asm/cpufeature.h>
#include <asm/cputype.h>
#include <asm/ptrace.h>
#include <asm/kvm_arm.h>
@@ -134,9 +135,38 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
return kvm_timer_vcpu_reset(vcpu);

+ * Configure the VTCR_EL2 for this VM. The VTCR value is common
+ * across all the physical CPUs on the system. We use system wide
+ * sanitised values to fill in different fields, except for Hardware
+ * Management of Access Flags. HA Flag is set unconditionally on
+ * all CPUs, as it is safe to run with or without the feature and
+ * the bit is RES0 on CPUs that don't support it.
+ */
int kvm_arm_config_vm(struct kvm *kvm, unsigned long type)
+ u64 vtcr = VTCR_EL2_FLAGS;

in include/asm/kvm_arm.h

I don't see T0SZ=24 encoded there and I don't see it set either in the
code below? For bisection purpose.

You're right, I am missing it here. I have fixed this up for v6,
with the following hunk.

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index e0c49377b771..fa897eafc2c9 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -147,6 +147,7 @@ int kvm_arm_config_vm(struct kvm *kvm, unsigned long
u64 vtcr = VTCR_EL2_FLAGS;
u64 parange;
+ u32 phys_shift;

if (type)
return -EINVAL;
@@ -156,6 +157,9 @@ int kvm_arm_config_vm(struct kvm *kvm, unsigned long
vtcr |= parange << VTCR_EL2_PS_SHIFT;

+ phys_shift = id_aa64mmfr0_parange_to_phys_shift(parange);
+ vtcr |= VTCR_EL2_T0SZ(phys_shift > 40 ? 40 : phys_shift);
* Enable the Hardware Access Flag management, unconditionally
* on all CPUs. The features is RES0 on CPUs without the support

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