On 08/01/15 12:30, Peter Maydell wrote:
> On 8 January 2015 at 11:59, Marc Zyngier <[email protected]> wrote:
>> @@ -180,10 +177,32 @@ static inline void coherent_cache_guest_page(struct
>> kvm_vcpu *vcpu, hva_t hva,
>> *
>> * VIVT caches are tagged using both the ASID and the VMID and
>> doesn't
>> * need any kind of flushing (DDI 0406C.b - Page B3-1392).
>> + *
>> + * We need to do this through a kernel mapping (using the
>> + * user-space mapping has proved to be the wrong
>> + * solution). For that, we need to kmap one page at a time,
>> + * and iterate over the range.
>> */
>> - if (icache_is_pipt()) {
>> - __cpuc_coherent_user_range(hva, hva + size);
>> - } else if (!icache_is_vivt_asid_tagged()) {
>> +
>> + VM_BUG_ON(size & PAGE_MASK);
>> +
>> + while (size) {
>> + void *va = kmap_atomic_pfn(pfn);
>> +
>> + if (!vcpu_has_cache_enabled(vcpu) || ipa_uncached)
>> + kvm_flush_dcache_to_poc(va, PAGE_SIZE);
>> +
>> + if (icache_is_pipt())
>> + __cpuc_coherent_user_range((unsigned long)va,
>> + (unsigned long)va +
>> PAGE_SIZE);
>> +
>> + size -= PAGE_SIZE;
>> + pfn++;
>> +
>> + kunmap_atomic(va);
>> + }
>
> If (vcpu_has_cache_enabled(vcpu) && !ipa_uncached && !icache_is_pipt())
> then we're going to run round this loop mapping and unmapping without
> actually doing anything. Is it worth hoisting that check out of the
> loop? (I think it's going to be the common case for a non-PIPT icache,
> right?)
Yup, that's a valid optimization.
>> + if (!icache_is_pipt() && !icache_is_vivt_asid_tagged()) {
>> /* any kind of VIPT cache */
>> __flush_icache_all();
>> }
>
> Can you remind me why it's OK not to flush the icache for an
> ASID tagged VIVT icache? Making this page coherent might actually
> be revealing a change in the instructions associated with the VA,
> mightn't it?
ASID cached VIVT icaches are also VMID tagged. It is thus impossible for
stale cache lines to come with a new page. And if by synchronizing the
caches you obtain a different instruction stream, it means you've
restored the wrong page.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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