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arm/arm64: KVM: Handle out-of-RAM cache maintenance as a NOP 

So far, our handling of cache maintenance by VA has been pretty
simple: Either the access is in the guest RAM and generates a S2
fault, which results in the page being mapped RW, or we go down
the io_mem_abort() path, and nuke the guest.

The first one is fine, but the second one is extremely weird.
Treating the CM as an I/O is wrong, and nothing in the ARM ARM
indicates that we should generate a fault for something that
cannot end-up in the cache anyway (even if the guest maps it,
it will keep on faulting at stage-2 for emulation).

So let's just skip this instruction, and let the guest get away
with it.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
hifive-unleashed-5.1
Marc Zyngier 2016-01-29 15:01:28 +00:00
parent 402f352876
commit 57c841f131
3 changed files with 26 additions and 0 deletions
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5
arch/arm/include/asm/kvm_emulate.h
View File

@ -138,6 +138,11 @@ static inline bool kvm_vcpu_dabt_iss1tw(struct kvm_vcpu *vcpu)
return kvm_vcpu_get_hsr(vcpu) & HSR_DABT_S1PTW;
}
static inline bool kvm_vcpu_dabt_is_cm(struct kvm_vcpu *vcpu)
{
return !!(kvm_vcpu_get_hsr(vcpu) & HSR_DABT_CM);
}
/* Get Access Size from a data abort */
static inline int kvm_vcpu_dabt_get_as(struct kvm_vcpu *vcpu)
{

16
arch/arm/kvm/mmu.c
View File

@ -1430,6 +1430,22 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
goto out_unlock;
}
/*
* Check for a cache maintenance operation. Since we
* ended-up here, we know it is outside of any memory
* slot. But we can't find out if that is for a device,
* or if the guest is just being stupid. The only thing
* we know for sure is that this range cannot be cached.
*
* So let's assume that the guest is just being
* cautious, and skip the instruction.
*/
if (kvm_vcpu_dabt_is_cm(vcpu)) {
kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
ret = 1;
goto out_unlock;
}
/*
* The IPA is reported as [MAX:12], so we need to
* complement it with the bottom 12 bits from the

5
arch/arm64/include/asm/kvm_emulate.h
View File

@ -189,6 +189,11 @@ static inline bool kvm_vcpu_dabt_iss1tw(const struct kvm_vcpu *vcpu)
return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_S1PTW);
}
static inline bool kvm_vcpu_dabt_is_cm(const struct kvm_vcpu *vcpu)
{
return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_CM);
}
static inline int kvm_vcpu_dabt_get_as(const struct kvm_vcpu *vcpu)
{
return 1 << ((kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SAS) >> ESR_ELx_SAS_SHIFT);