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KVM: arm64: nv: Handle CNTHCTL_EL2 specially

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Accessing CNTHCTL_EL2 is fraught with danger if running with
HCR_EL2.E2H=1: half of the bits are held in CNTKCTL_EL1, and
thus can be changed behind our back, while the rest lives
in the CNTHCTL_EL2 shadow copy that is memory-based.

Yes, this is a lot of fun!

Make sure that we merge the two on read access, while we can
write to CNTKCTL_EL1 in a more straightforward manner.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241023145345.1613824-7-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Marc Zyngier 2024-10-23 15:53:14 +01:00 committed by Oliver Upton
parent dfeb916869
commit 164b5e20cd
2 changed files with 31 additions and 0 deletions
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28
arch/arm64/kvm/sys_regs.c
View File

@ -157,6 +157,21 @@ u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
if (!is_hyp_ctxt(vcpu))
goto memory_read;
/*
* CNTHCTL_EL2 requires some special treatment to
* account for the bits that can be set via CNTKCTL_EL1.
*/
switch (reg) {
case CNTHCTL_EL2:
if (vcpu_el2_e2h_is_set(vcpu)) {
val = read_sysreg_el1(SYS_CNTKCTL);
val &= CNTKCTL_VALID_BITS;
val |= __vcpu_sys_reg(vcpu, reg) & ~CNTKCTL_VALID_BITS;
return val;
}
break;
}
/*
* If this register does not have an EL1 counterpart,
* then read the stored EL2 version.
@ -207,6 +222,19 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
*/
__vcpu_sys_reg(vcpu, reg) = val;
switch (reg) {
case CNTHCTL_EL2:
/*
* If E2H=0, CNHTCTL_EL2 is a pure shadow register.
* Otherwise, some of the bits are backed by
* CNTKCTL_EL1, while the rest is kept in memory.
* Yes, this is fun stuff.
*/
if (vcpu_el2_e2h_is_set(vcpu))
write_sysreg_el1(val, SYS_CNTKCTL);
return;
}
/* No EL1 counterpart? We're done here.? */
if (reg == el1r)
return;

3
include/kvm/arm_arch_timer.h
View File

@ -147,6 +147,9 @@ u64 timer_get_cval(struct arch_timer_context *ctxt);
void kvm_timer_cpu_up(void);
void kvm_timer_cpu_down(void);
/* CNTKCTL_EL1 valid bits as of DDI0487J.a */
#define CNTKCTL_VALID_BITS (BIT(17) | GENMASK_ULL(9, 0))
static inline bool has_cntpoff(void)
{
return (has_vhe() && cpus_have_final_cap(ARM64_HAS_ECV_CNTPOFF));