Re: [PATCH] KVM: PPC: Book3S HV: Fix reverse map real-mode address lookup with huge vmalloc

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

Christophe Leroy <christophe.leroy@csgroup.eu> writes:

> Nicholas Piggin <npiggin@gmail.com> a écrit :
>
>> real_vmalloc_addr() does not currently work for huge vmalloc, which is
>> what the reverse map can be allocated with for radix host, hash guest.
>>
>> Add huge page awareness to the function.
>>
>> Fixes: 8abddd968a30 ("powerpc/64s/radix: Enable huge vmalloc mappings")
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>>  arch/powerpc/kvm/book3s_hv_rm_mmu.c | 17 ++++++++++++-----
>>  1 file changed, 12 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c  
>> b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
>> index 7af7c70f1468..5f68cb5cc009 100644
>> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
>> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
>> @@ -26,16 +26,23 @@
>>  static void *real_vmalloc_addr(void *x)
>>  {
>>  	unsigned long addr = (unsigned long) x;
>> +	unsigned long mask;
>> +	int shift;
>>  	pte_t *p;
>> +
>>  	/*
>> -	 * assume we don't have huge pages in vmalloc space...
>> -	 * So don't worry about THP collapse/split. Called
>> -	 * Only in realmode with MSR_EE = 0, hence won't need irq_save/restore.
>> +	 * This is called only in realmode with MSR_EE = 0, hence won't need
>> +	 * irq_save/restore around find_init_mm_pte.
>>  	 */
>> -	p = find_init_mm_pte(addr, NULL);
>> +	p = find_init_mm_pte(addr, &shift);
>>  	if (!p || !pte_present(*p))
>>  		return NULL;
>> -	addr = (pte_pfn(*p) << PAGE_SHIFT) | (addr & ~PAGE_MASK);
>> +	if (!shift)
>> +		shift = PAGE_SHIFT;
>> +
>> +	mask = (1UL << shift) - 1;
>> +	addr = (pte_pfn(*p) << PAGE_SHIFT) | (addr & mask);
>
> Looks strange, before we have ~MASK now we have mask without the ~

#define PAGE_MASK      (~((1 << PAGE_SHIFT) - 1))

-aneesh