Re: [PATCH 10/10] arm: KVM: Use common implementation for all flushes to PoC

Marc Zyngier
2017-10-17T12:40:00Z

On 16/10/17 21:06, Christoffer Dall wrote:
> On Mon, Oct 09, 2017 at 04:20:32PM +0100, Marc Zyngier wrote:
>> We currently have no less than three implementations for the
>> "flush to PoC" code. Let standardize on a single one. This
>> requires a bit of unpleasant moving around, and relies on
>> __kvm_flush_dcache_pte and co being #defines so that they can
>> call into coherent_dcache_guest_page...
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>> arch/arm/include/asm/kvm_mmu.h | 28 ++++------------------------
>> virt/kvm/arm/mmu.c | 20 ++++++++++----------
>> 2 files changed, 14 insertions(+), 34 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
>> index 5f1ac88a5951..011b0db85c02 100644
>> --- a/arch/arm/include/asm/kvm_mmu.h
>> +++ b/arch/arm/include/asm/kvm_mmu.h
>> @@ -235,31 +235,11 @@ static inline void __coherent_icache_guest_page(kvm_pfn_t pfn,
>> }
>> }
>>
>> -static inline void __kvm_flush_dcache_pte(pte_t pte)
>> -{
>> - void *va = kmap_atomic(pte_page(pte));
>> -
>> - kvm_flush_dcache_to_poc(va, PAGE_SIZE);
>> -
>> - kunmap_atomic(va);
>> -}
>> -
>> -static inline void __kvm_flush_dcache_pmd(pmd_t pmd)
>> -{
>> - unsigned long size = PMD_SIZE;
>> - kvm_pfn_t pfn = pmd_pfn(pmd);
>> -
>> - while (size) {
>> - void *va = kmap_atomic_pfn(pfn);
>> +#define __kvm_flush_dcache_pte(p) \
>> + coherent_dcache_guest_page(pte_pfn((p)), PAGE_SIZE)
>>
>> - kvm_flush_dcache_to_poc(va, PAGE_SIZE);
>> -
>> - pfn++;
>> - size -= PAGE_SIZE;
>> -
>> - kunmap_atomic(va);
>> - }
>> -}
>> +#define __kvm_flush_dcache_pmd(p) \
>> + coherent_dcache_guest_page(pmd_pfn((p)), PMD_SIZE)
>
> Why can't these just be static inlines which call
> __coherent_dcache_guest_page already in the header file directly?

Because if we do that, we get a significant code expansion in the
resulting binary (all the call sites end up having a copy of that function.

> I'm really not too crazy about these #defines.

Neither am I. But actually, this patch is completely wrong. Using the
same functions as the guest cleaning doesn't provide the guarantees
documented next to unmap_stage2_ptes, as we need a clean+invalidate, not
just a clean.

I'll rework this patch (or just drop it).

> In fact, why do we need the coherent_Xcache_guest_page static
> indirection functions in mmu.c in the first place?

Code expansion. That's the only reason.

Thanks,

M.
--
Jazz is not dead. It just smells funny...