Michael Neuling <mi...@neuling.org> writes:
> Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com> wrote:
>
>> From: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
>>
>> We can find pte that are splitting while walking page tables. Return
>> None pte in that case.
>
> Can you expand on this more please. There are a lot of details below
> like removing a ldarx/stdcx loop that should be better described here.
>
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
>> ---
>> arch/powerpc/include/asm/kvm_book3s_64.h | 51
>> ++++++++++++++++++--------------
>> arch/powerpc/kvm/book3s_64_mmu_hv.c | 7 +++--
>> arch/powerpc/kvm/book3s_hv_rm_mmu.c | 4 +--
>> 3 files changed, 34 insertions(+), 28 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h
>> b/arch/powerpc/include/asm/kvm_book3s_64.h
>> index 9c1ff33..ce20f7e 100644
>> --- a/arch/powerpc/include/asm/kvm_book3s_64.h
>> +++ b/arch/powerpc/include/asm/kvm_book3s_64.h
>> @@ -162,33 +162,40 @@ static inline int hpte_cache_flags_ok(unsigned long
>> ptel, unsigned long io_type)
>> * Lock and read a linux PTE. If it's present and writable, atomically
>> * set dirty and referenced bits and return the PTE, otherwise return 0.
>
> This is comment still valid now the ldarx/stdcx is gone?
In a way yes. Instead of lock and read as it was before, it is now done
via cmpxchg which still use ldarx/stdcx
>
>> */
>> -static inline pte_t kvmppc_read_update_linux_pte(pte_t *p, int writing)
>> +static inline pte_t kvmppc_read_update_linux_pte(pte_t *ptep, int writing,
>> + unsigned int hugepage)
>> {
>> - pte_t pte, tmp;
>> -
>> - /* wait until _PAGE_BUSY is clear then set it atomically */
>> - __asm__ __volatile__ (
>> - "1: ldarx %0,0,%3\n"
>> - " andi. %1,%0,%4\n"
>> - " bne- 1b\n"
>> - " ori %1,%0,%4\n"
>> - " stdcx. %1,0,%3\n"
>> - " bne- 1b"
>> - : "=&r" (pte), "=&r" (tmp), "=m" (*p)
>> - : "r" (p), "i" (_PAGE_BUSY)
>> - : "cc");
>> -
>> - if (pte_present(pte)) {
>> - pte = pte_mkyoung(pte);
>> - if (writing && pte_write(pte))
>> - pte = pte_mkdirty(pte);
>> - }
>> + pte_t old_pte, new_pte = __pte(0);
>> +repeat:
>> + do {
>> + old_pte = pte_val(*ptep);
>> + /*
>> + * wait until _PAGE_BUSY is clear then set it atomically
>> + */
>> + if (unlikely(old_pte & _PAGE_BUSY))
>> + goto repeat;
>
> continue here? Please don't create looping primitives.
No that would be wrong. (I did that in an earlier version :).We really
don't want the below cmpxchg to run if we find _PAGE_BUSY.
>
>> +
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> + /* If hugepage and is trans splitting return None */
>> + if (unlikely(hugepage &&
>> + pmd_trans_splitting(pte_pmd(old_pte))))
>
> Comment looks much like the code... seems redundant.
>
>> + return __pte(0);
>> +#endif
>>
>> - *p = pte; /* clears _PAGE_BUSY */
>> + /* If pte is not present return None */
>> + if (unlikely(!(old_pte & _PAGE_PRESENT)))
>> + return __pte(0);
>>
>> - return pte;
>> + new_pte = pte_mkyoung(old_pte);
>> + if (writing && pte_write(old_pte))
>> + new_pte = pte_mkdirty(new_pte);
>> +
>> + } while (old_pte != __cmpxchg_u64((unsigned long *)ptep,
>> + old_pte, new_pte));
>> + return new_pte;
>> }
>>
>> +
>
> Whitespace
>
>> /* Return HPTE cache control bits corresponding to Linux pte bits */
>> static inline unsigned long hpte_cache_bits(unsigned long pte_val)
>> {
>> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c
>> b/arch/powerpc/kvm/book3s_64_mmu_hv.c
>> index 5880dfb..e1a9415 100644
>> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
>> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
>> @@ -675,6 +675,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run,
>> struct kvm_vcpu *vcpu,
>> }
>> /* if the guest wants write access, see if that is OK */
>> if (!writing && hpte_is_writable(r)) {
>> + unsigned int shift;
>> pte_t *ptep, pte;
>>
>> /*
>> @@ -683,9 +684,9 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run,
>> struct kvm_vcpu *vcpu,
>> */
>> rcu_read_lock_sched();
>> ptep = find_linux_pte_or_hugepte(current->mm->pgd,
>> - hva, NULL);
>> - if (ptep && pte_present(*ptep)) {
>> - pte = kvmppc_read_update_linux_pte(ptep, 1);
>> + hva, &shift);
>> + if (ptep) {
>> + pte = kvmppc_read_update_linux_pte(ptep, 1,
>> shift);
>> if (pte_write(pte))
>> write_ok = 1;
>> }
>> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
>> b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
>> index dcf892d..39ae723 100644
>> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
>> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
>> @@ -150,9 +150,7 @@ static pte_t lookup_linux_pte(pgd_t *pgdir, unsigned
>> long hva,
>> *pte_sizep = PAGE_SIZE;
>> if (ps > *pte_sizep)
>> return __pte(0);
>> - if (!pte_present(*ptep))
>> - return __pte(0);
>> - return kvmppc_read_update_linux_pte(ptep, writing);
>> + return kvmppc_read_update_linux_pte(ptep, writing, shift);
>
> 'shift' goes into the new 'hugepage' parameter? Doesn't seem logical?
> Can we harmonise the name to make it less confusing?
>
it is actually the shift bits represending hugepage size. We set it to 0
if we don't find hugepage in find_linux_pte_or_hugepte. May be something
like hugepage_shift is better ?
-aneesh
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