On Mon, Nov 10, 2014 at 12:15 PM, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
On 10 November 2014 11:57, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote:
> On Mon, Nov 10, 2014 at 09:33:55AM +0100, Ard Biesheuvel wrote:
>> Instead of using kvm_is_mmio_pfn() to decide whether a host region
>> should be stage 2 mapped with device attributes, add a new static
>> function kvm_is_device_pfn() that disregards RAM pages with the
>> reserved bit set, as those should usually not be mapped as device
>> memory.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>> ---
>> arch/arm/kvm/mmu.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 57a403a5c22b..b007438242e2 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -834,6 +834,11 @@ static bool kvm_is_write_fault(struct kvm_vcpu *vcpu)
>> return kvm_vcpu_dabt_iswrite(vcpu);
>> }
>>
>> +static bool kvm_is_device_pfn(unsigned long pfn)
>> +{
>> + return !pfn_valid(pfn);
>> +}
>
> So this works for Magnus' use case, because a device tree memreserve
> results in reserved, but valid, existing pages being backed by a struct
> page?
>
That is the idea, yes, but it would be good if he could confirm that
it works as expected.
Also, there may be some corner cases where pfn_valid returns false for
regions that are in fact mapped as MT_NORMAL by the host kernel, i.e.,
UEFI configuration tables, for instance, so this test may require
further refinement. But it at least eliminates the false positives for
plain memreserve regions.
>> +
>> static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> struct kvm_memory_slot *memslot, unsigned long hva,
>> unsigned long fault_status)
>> @@ -904,7 +909,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> if (is_error_pfn(pfn))
>> return -EFAULT;
>>
>> - if (kvm_is_mmio_pfn(pfn))
>> + if (kvm_is_device_pfn(pfn))
>> mem_type = PAGE_S2_DEVICE;
>>
>> spin_lock(&kvm->mmu_lock);
>> --
>> 1.8.3.2
>>
>
> If my understanding above is correct, then:
>
> Acked-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
I tried it on my system (LSI Axxia AXM5516) with a memreserved cache-coherent IO region and it works. It does not work without the patch.
Ard, Christoffer and Mario, thanks for your help. Highly appreciated.
Tested-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxxxxxx>
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