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KVM: arm64: nv: Honor guest hypervisor's FP/SVE traps in CPTR_EL2

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Start folding the guest hypervisor's FP/SVE traps into the value
programmed in hardware. Note that as of writing this is dead code, since
KVM does a full put() / load() for every nested exception boundary which
saves + flushes the FP/SVE state.

However, this will become useful when we can keep the guest's FP/SVE
state alive across a nested exception boundary and the host no longer
needs to conservatively program traps.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240620164653.1130714-12-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Oliver Upton
2024-06-20 16:46:48 +00:00
parent 0cfc85b8f5
commit 5326303bb7
1 changed files with 31 additions and 0 deletions
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31
arch/arm64/kvm/hyp/vhe/switch.c
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@@ -67,6 +67,8 @@ static u64 __compute_hcr(struct kvm_vcpu *vcpu)
static void __activate_cptr_traps(struct kvm_vcpu *vcpu)
{
u64 cptr;
/*
* With VHE (HCR.E2H == 1), accesses to CPACR_EL1 are routed to
* CPTR_EL2. In general, CPACR_EL1 has the same layout as CPTR_EL2,
@@ -85,6 +87,35 @@ static void __activate_cptr_traps(struct kvm_vcpu *vcpu)
__activate_traps_fpsimd32(vcpu);
}
/*
* Layer the guest hypervisor's trap configuration on top of our own if
* we're in a nested context.
*/
if (!vcpu_has_nv(vcpu) || is_hyp_ctxt(vcpu))
goto write;
cptr = vcpu_sanitised_cptr_el2(vcpu);
/*
* Pay attention, there's some interesting detail here.
*
* The CPTR_EL2.xEN fields are 2 bits wide, although there are only two
* meaningful trap states when HCR_EL2.TGE = 0 (running a nested guest):
*
* - CPTR_EL2.xEN = x0, traps are enabled
* - CPTR_EL2.xEN = x1, traps are disabled
*
* In other words, bit[0] determines if guest accesses trap or not. In
* the interest of simplicity, clear the entire field if the guest
* hypervisor has traps enabled to dispel any illusion of something more
* complicated taking place.
*/
if (!(SYS_FIELD_GET(CPACR_ELx, FPEN, cptr) & BIT(0)))
val &= ~CPACR_ELx_FPEN;
if (!(SYS_FIELD_GET(CPACR_ELx, ZEN, cptr) & BIT(0)))
val &= ~CPACR_ELx_ZEN;
write:
write_sysreg(val, cpacr_el1);
}