From: Christoffer Dall [c.dall at virtualopensystems.com]
> On Tue, May 29, 2012 at 5:47 AM, Marc Zyngier <marc.zyngier at arm.com>
wrote:
>> Rework the HYP idmap code to be more consistent with what the kernel
>> does:
>>
>> - Move the HYP pgd to the core code (so it can benefit to other
>> hypervisors)
>> - Populate this pgd with an identity mapping of the code contained
>> in the .hyp_idmap.text section
>> - Offer a method to drop the this identity mapping
> the this?
>> - Make all the above depend on CONFIG_ARM_VIRT_EXT
>>
>> This makes the core code more generic, and remove some of the
>> clutter from the KVM init.
> s/remove/removes/
Thanks. Blame it on the HK jet-lag... ;-)
> [snip]
>
>> diff --git a/arch/arm/include/asm/pgtable.h
>> b/arch/arm/include/asm/pgtable.h
>> index fffc01f..9f549c6 100644
>> --- a/arch/arm/include/asm/pgtable.h
>> +++ b/arch/arm/include/asm/pgtable.h
>> @@ -315,9 +315,10 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t
>> newprot)
>>
>> #define pgtable_cache_init() do { } while (0)
>>
>> -#ifdef CONFIG_KVM_ARM_HOST
>> -void hyp_idmap_add(pgd_t *, unsigned long, unsigned long);
>> -void hyp_idmap_del(pgd_t *pgd, unsigned long addr, unsigned long end);
>> +#ifdef CONFIG_ARM_VIRT_EXT
>> +extern pgd_t *hyp_pgd;
>
> hmm, I'm a bit worried about limiting the kernel to user only one
> mapping in Hyp mode in general. What if there were several uses of
> Hyp-mode on a given host system? Remapping the same virtual addresses
> involves switching to Hyp-mode to flush TLBs etc. (iirc), so that
> sounds almost impossible.
Nothing prevents you from using a different set of page tables. The kernel
provides you with one that contains the identity mapping, and KVM can use
it. Or not. When it comes to sharing HYP mode, this patch doesn't really
affect the current situation - it is hard and pretty much unsupported.
> This approach actually seems less clean than the previous approach,
> which was nicely contained to the use of KVM. Why would this be a
> potential problem to merge?
The main problem with this approach is that the kernel has moved away from
it, and now uses a section-based identity mapping (users of the identity
mapping don't have to populate the idmap page tables, as it is all done at
build time). Bringing back the old mechanism feels like a regression, while
this patch aligns the use pattern of the various sets of page tables. It
also removes a nice chunk of KVM init code.
M.
--
Fast, cheap, reliable. Pick two.
