On 18.07.2013, at 19:17, Scott Wood wrote:
> On 07/18/2013 08:19:03 AM, Bharat Bhushan wrote:
>> If there is a struct page for the requested mapping then it's
>> normal RAM and the mapping is set to "M" bit (coherent, cacheable)
>> otherwise this is treated as I/O and we set "I + G" (cache inhibited,
>> guarded)
>> This helps setting proper TLB mapping for direct assigned device
>> Signed-off-by: Bharat Bhushan <bharat.bhus...@freescale.com>
>> ---
>> v2: some cleanup and added comment
>> -
>> arch/powerpc/kvm/e500_mmu_host.c | 23 ++++++++++++++++++-----
>> 1 files changed, 18 insertions(+), 5 deletions(-)
>> diff --git a/arch/powerpc/kvm/e500_mmu_host.c
>> b/arch/powerpc/kvm/e500_mmu_host.c
>> index 1c6a9d7..02eb973 100644
>> --- a/arch/powerpc/kvm/e500_mmu_host.c
>> +++ b/arch/powerpc/kvm/e500_mmu_host.c
>> @@ -64,13 +64,26 @@ static inline u32 e500_shadow_mas3_attrib(u32 mas3, int
>> usermode)
>> return mas3;
>> }
>> -static inline u32 e500_shadow_mas2_attrib(u32 mas2, int usermode)
>> +static inline u32 e500_shadow_mas2_attrib(u32 mas2, pfn_t pfn)
>> {
>> + u32 mas2_attr;
>> +
>> + mas2_attr = mas2 & MAS2_ATTRIB_MASK;
>> +
>> + /*
>> + * RAM is always mappable on e500 systems, so this is identical
>> + * to kvm_is_mmio_pfn(), just without its overhead.
>> + */
>> + if (!pfn_valid(pfn)) {
>
> Please use page_is_ram(), which is what gets used when setting the WIMG for
> the host userspace mapping. We want to make sure the two are consistent.
>
>> + /* Pages not managed by Kernel are treated as I/O, set I + G */
>> + mas2_attr |= MAS2_I | MAS2_G;
>> #ifdef CONFIG_SMP
>> - return (mas2 & MAS2_ATTRIB_MASK) | MAS2_M;
>> -#else
>> - return mas2 & MAS2_ATTRIB_MASK;
>> + } else {
>> + /* Kernel managed pages are actually RAM so set "M" */
>> + mas2_attr |= MAS2_M;
>> #endif
>
> Likewise, we want to make sure this matches the host entry. Unfortunately,
> this is a bit of a mess already. 64-bit booke appears to always set MAS2_M
> for TLB0 mappings. The initial KERNELBASE mapping on boot uses M_IF_SMP, and
> the settlbcam() that (IIRC) replaces it uses _PAGE_COHERENT. 32-bit always
> uses _PAGE_COHERENT, except that initial KERNELBASE mapping. _PAGE_COHERENT
> appears to be set based on CONFIG_SMP || CONFIG_PPC_STD_MMU (the latter
> config clears _PAGE_COHERENT in the non-CPU_FTR_NEED_COHERENT case).
>
> As for what we actually want to happen, there are cases when we want M to be
> set for non-SMP. One such case is AMP, where CPUs may be sharing memory even
> if the Linux instance only runs on one CPU (this is not hypothetical, BTW).
> It's also possible that we encounter a hardware bug that requires MAS2_M,
> similar to what some of our non-booke chips require.
How about we always set M then for RAM?
Alex
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