Messages in this thread | | | Subject | Re: [PATCH v5 16/18] kvm: arm64: Set a limit on the IPA size | From | Suzuki K Poulose <> | Date | Tue, 25 Sep 2018 12:10:20 +0100 |
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On 09/25/2018 10:59 AM, Auger Eric wrote: > Hi Suzuki, > > On 9/17/18 12:41 PM, Suzuki K Poulose wrote: >> So far we have restricted the IPA size of the VM to the default >> value (40bits). Now that we can manage the IPA size per VM and >> support dynamic stage2 page tables, we can allow VMs to have >> larger IPA. This patch introduces a the maximum IPA size >> supported on the host. > to be reworded > This is decided by the following factors :
Sure
>> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c >> index 51ecf0f7c912..76972b19bdd7 100644 >> --- a/arch/arm64/kvm/reset.c >> +++ b/arch/arm64/kvm/reset.c >> @@ -34,6 +34,9 @@ >> #include <asm/kvm_coproc.h> >> #include <asm/kvm_mmu.h> >> >> +/* Maximum phys_shift supported for any VM on this host */ >> +static u32 kvm_ipa_limit; >> + >> /* >> * ARMv8 Reset Values >> */ >> @@ -135,6 +138,46 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) >> return kvm_timer_vcpu_reset(vcpu); >> } >> >> +void kvm_set_ipa_limit(void) >> +{ >> + unsigned int ipa_max, va_max, parange; >> + >> + parange = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1) & 0x7; >> + ipa_max = id_aa64mmfr0_parange_to_phys_shift(parange); >> + >> + /* Raise the limit to the default size for backward compatibility */ >> + if (ipa_max < KVM_PHYS_SHIFT) { >> + WARN_ONCE(1, >> + "PARange is %d bits, unsupported configuration!", >> + ipa_max); >> + ipa_max = KVM_PHYS_SHIFT; > I don't really get what does happen in this case. The CPU cannot handle > PA up to ipa_max so can the VM run properly? In case it is a > showstopper, kvm_set_ipa_limit should return an error, cascaded by > init_common_resources. Otherwise the warning message may be reworded.
I think this was a warning added to warn against the older Foundation model which had a 36bit PA size. So the VTCR was progammed with a 36bit limit, while the KVM guest was allowed to create 40bit IPA space, though it wouldn't fly well if someone tried to.
With this series, I think we may expose the real IPA_MAX (which could be < 40bit) and warn the user if someone tried to create a VM with 40bit IPA (vm_type == 0) and let the call succeed (for the sake of ABI).
Marc, Christoffer, Eric
Thoughts ?
>> + } >> + >> + /* Clamp it to the PA size supported by the kernel */ >> + ipa_max = (ipa_max > PHYS_MASK_SHIFT) ? PHYS_MASK_SHIFT : ipa_max; >> + /* >> + * Since our stage2 table is dependent on the stage1 page table code, >> + * we must always honor the following condition: >> + * >> + * Number of levels in Stage1 >= Number of levels in Stage2. >> + * >> + * So clamp the ipa limit further down to limit the number of levels. >> + * Since we can concatenate upto 16 tables at entry level, we could >> + * go upto 4bits above the maximum VA addressible with the current > addressable?
Sure
>> + * number of levels. >> + */ >> + va_max = PGDIR_SHIFT + PAGE_SHIFT - 3; >> + va_max += 4; >> + >> + if (va_max < ipa_max) { >> + kvm_info("Limiting IPA limit to %dbytes due to host VA bits limitation\n", >> + va_max); >> + ipa_max = va_max; > you have a trace for this limitation but none for the comparison against > PHYS_MASK_SHIFT.
May be I could add a message which only mentions what is the limiting factor kernel VA vs kernel PA support
>> + } >> + >> + kvm_ipa_limit = ipa_max; >> +} >> + >> /* >> * Configure the VTCR_EL2 for this VM. The VTCR value is common >> * across all the physical CPUs on the system. We use system wide >> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c >> index 43e716bc3f08..631f9a3ad99a 100644 >> --- a/virt/kvm/arm/arm.c >> +++ b/virt/kvm/arm/arm.c >> @@ -1413,6 +1413,8 @@ static int init_common_resources(void) >> kvm_vmid_bits = kvm_get_vmid_bits(); >> kvm_info("%d-bit VMID\n", kvm_vmid_bits); >> >> + kvm_set_ipa_limit(); > As we have a kvm_info for the supported vmid_bits, may be good to output > the max IPA size supported by the host whatever the applied clamps?
Sure, will do that.
Thanks Suzuki
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