Subject: [PATCH v4] arm64: fix VTTBR_BADDR_MASK

From: [email-masked] (Joel Schopp)
Date: Tue, 19 Aug 2014 09:05:09 -0500

On 08/19/2014 07:22 AM, Christoffer Dall wrote:
> On Mon, Aug 18, 2014 at 03:30:58PM -0500, Joel Schopp wrote:
>>  #endif /* __ARM_KVM_MMU_H__ */
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 16e7994..70f0f02 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -521,6 +521,7 @@ int create_hyp_io_mappings(void *from, void *to, phys_addr_t phys_addr)
>>   */
>>  int kvm_alloc_stage2_pgd(struct kvm *kvm)
>>  {
>> +	unsigned int s2_pgds, s2_pgd_order;
>>  	pgd_t *pgd;
>>  
>>  	if (kvm->arch.pgd != NULL) {
>> @@ -528,10 +529,18 @@ int kvm_alloc_stage2_pgd(struct kvm *kvm)
>>  		return -EINVAL;
>>  	}
>>  
>> -	pgd = (pgd_t *)__get_free_pages(GFP_KERNEL, S2_PGD_ORDER);
>> +	s2_pgds = (1 << (kvm_get_phys_addr_shift() - PGDIR_SHIFT));
>> +	s2_pgd_order = get_order(s2_pgds * sizeof(pgd_t));
>> +
>> +	pgd = (pgd_t *)__get_free_pages(GFP_KERNEL, s2_pgd_order);
>>  	if (!pgd)
>>  		return -ENOMEM;
>>  
>> +	if ((unsigned long)pgd & ~vttbr_baddr_mask) {
>> +		kvm_err("Stage-2 pgd not correctly aligned: %p\n", pgd);
>> +		return -EFAULT;
>> +	}
>>
>>
>> There are two problems that I've found here.  The first problem is that
>> vttbr_baddr_mask isn't allocated yet at this point in the code.
> allocated? you mean assigned?
> aren't you setting vttbr_baddr_mask in kvm_arch_init()?  that's
> certainly called before kvm_arch_init_vm().
Yes, I mean assigned, at least I got the first letter correct :)  All I
know is that vttbr_baddr_mask was still zero and checking for zero and
calling the set function gave it a value.
>
>
>> The
>> second problem is that pgd is a virtual address, ie pgd ==
>> 0xfffffe03bbb40000 while the vttbr masks off the high bits for a
>> physical address, ie vttbr_baddr_mask=0x00007ffffffe0000 .  Even
>> correcting for those issues I haven't been able to make this check work
>> properly.  I'll resend v5 the patch with all the other suggested changes.
>>
> What are the issues that you face?  Iow. what is the alignment of the
> returned physical address?
>
> (You should be able to just to virt_to_phys(pgd) and use that to test
> for the vttbr_baddr_mask).
The addresses above are actually from my system, 64K page aligned on a
64K page kernel.  I did use virt_to_phys() and the kernel got a null
dereference and paniced, I didn't trace down where the panic was occuring.

> Thanks,
> -Christoffer