Subject: [PATCH v2 1/3] arm64: KVM: Implement 48 VA support for KVM EL2 and Stage-2

From: [email-masked] (Marc Zyngier)
Date: Wed, 08 Oct 2014 11:27:39 +0100

On 08/10/14 10:47, Christoffer Dall wrote:
> On Wed, Oct 08, 2014 at 10:34:31AM +0100, Marc Zyngier wrote:
>> On 07/10/14 20:39, Christoffer Dall wrote:
>>> On Tue, Oct 07, 2014 at 02:28:43PM +0100, Marc Zyngier wrote:
>>>> On 07/10/14 11:48, Catalin Marinas wrote:
>>>>> On Mon, Oct 06, 2014 at 09:30:25PM +0100, Christoffer Dall wrote:
>>>>>> +/**
>>>>>> + * kvm_prealloc_hwpgd - allocate inital table for VTTBR
>>>>>> + * @kvm:       The KVM struct pointer for the VM.
>>>>>> + * @pgd:       The kernel pseudo pgd
>>>>>> + *
>>>>>> + * When the kernel uses more levels of page tables than the guest, we allocate
>>>>>> + * a fake PGD and pre-populate it to point to the next-level page table, which
>>>>>> + * will be the real initial page table pointed to by the VTTBR.
>>>>>> + *
>>>>>> + * When KVM_PREALLOC_LEVEL==2, we allocate a single page for the PMD and
>>>>>> + * the kernel will use folded pud.  When KVM_PREALLOC_LEVEL==1, we
>>>>>> + * allocate 2 consecutive PUD pages.
>>>>>> + */
>>>>>> +#if defined(CONFIG_ARM64_64K_PAGES) && CONFIG_ARM64_PGTABLE_LEVELS == 3
>>>>>> +#define KVM_PREALLOC_LEVEL     2
>>>>>> +#define PTRS_PER_S2_PGD                1
>>>>>> +#define S2_PGD_ORDER           get_order(PTRS_PER_S2_PGD * sizeof(pgd_t))
>>>>>
>>>>> I agree that my magic equation wasn't readable ;) (I had troubles
>>>>> re-understanding it as well), but you also have some constants here that
>>>>> are not immediately obvious where you got to them from. IIUC,
>>>>> KVM_PREALLOC_LEVEL == 2 here means that the hardware only understands
>>>>> stage 2 pmd and pte. I guess you could look into the ARM ARM tables but
>>>>> it's still not clear.
>>>>>
>>>>> Let's look at PTRS_PER_S2_PGD as I think it's simpler. My proposal was:
>>>>>
>>>>> #if PGDIR_SHIFT > KVM_PHYS_SHIFT
>>>>> #define PTRS_PER_S2_PGD                     (1)
>>>>> #else
>>>>> #define PTRS_PER_S2_PGD                     (1 << (KVM_PHYS_SHIFT - PGDIR_SHIFT))
>>>>> #endif
>>>>>
>>>>> In this case PGDIR_SHIFT is 42, so we get PTRS_PER_S2_PGD == 1. The 4K
>>>>> and 4 levels case below is also correct.
>>>>>
>>>>> The KVM start level calculation, we could assume that KVM needs either
>>>>> host levels or host levels - 1 (unless we go for some weirdly small
>>>>> KVM_PHYS_SHIFT). So we could define them KVM_PREALLOC_LEVEL as:
>>>>>
>>>>> #if PTRS_PER_S2_PGD <= 16
>>>>> #define KVM_PREALLOC_LEVEL  (4 - CONFIG_ARM64_PGTABLE_LEVELS + 1)
>>>>> #else
>>>>> #define KVM_PREALLOC_LEVEL  (0)
>>>>> #endif
>>>>>
>>>>> Basically if you can concatenate 16 or less pages at the level below the
>>>>> top, the architecture does not allow a small top level. In this case,
>>>>> (4 - CONFIG_ARM64_PGTABLE_LEVELS) represents the first level for the
>>>>> host and we add 1 to go to the next level for KVM stage 2 when
>>>>> PTRS_PER_S2_PGD is 16 or less. We use 0 when we don't need to
>>>>> preallocate.
>>>>
>>>> I think this makes the whole thing clearer (at least for me), as it
>>>> makes the relationship between KVM_PREALLOC_LEVEL and
>>>> CONFIG_ARM64_PGTABLE_LEVELS explicit (it wasn't completely obvious to me
>>>> initially).
>>>
>>> Agreed.
>>>
>>>>
>>>>>> +static inline int kvm_prealloc_hwpgd(struct kvm *kvm, pgd_t *pgd)
>>>>>> +{
>>>>>> +       pud_t *pud;
>>>>>> +       pmd_t *pmd;
>>>>>> +
>>>>>> +       pud = pud_offset(pgd, 0);
>>>>>> +       pmd = (pmd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 0);
>>>>>> +
>>>>>> +       if (!pmd)
>>>>>> +               return -ENOMEM;
>>>>>> +       pud_populate(NULL, pud, pmd);
>>>>>> +
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static inline void kvm_free_hwpgd(struct kvm *kvm)
>>>>>> +{
>>>>>> +       pgd_t *pgd = kvm->arch.pgd;
>>>>>> +       pud_t *pud = pud_offset(pgd, 0);
>>>>>> +       pmd_t *pmd = pmd_offset(pud, 0);
>>>>>> +       free_pages((unsigned long)pmd, 0);
>>>>>> +}
>>>>>> +
>>>>>> +static inline phys_addr_t kvm_get_hwpgd(struct kvm *kvm)
>>>>>> +{
>>>>>> +       pgd_t *pgd = kvm->arch.pgd;
>>>>>> +       pud_t *pud = pud_offset(pgd, 0);
>>>>>> +       pmd_t *pmd = pmd_offset(pud, 0);
>>>>>> +       return virt_to_phys(pmd);
>>>>>> +
>>>>>> +}
>>>>>> +#elif defined(CONFIG_ARM64_4K_PAGES) && CONFIG_ARM64_PGTABLE_LEVELS == 4
>>>>>> +#define KVM_PREALLOC_LEVEL     1
>>>>>> +#define PTRS_PER_S2_PGD                2
>>>>>> +#define S2_PGD_ORDER           get_order(PTRS_PER_S2_PGD * sizeof(pgd_t))
>>>>>
>>>>> Here PGDIR_SHIFT is 39, so we get PTRS_PER_S2_PGD == (1 << (40 - 39))
>>>>> which is 2 and KVM_PREALLOC_LEVEL == 1.
>>>>>
>>>>>> +static inline int kvm_prealloc_hwpgd(struct kvm *kvm, pgd_t *pgd)
>>>>>> +{
>>>>>> +       pud_t *pud;
>>>>>> +
>>>>>> +       pud = (pud_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
>>>>>> +       if (!pud)
>>>>>> +               return -ENOMEM;
>>>>>> +       pgd_populate(NULL, pgd, pud);
>>>>>> +       pgd_populate(NULL, pgd + 1, pud + PTRS_PER_PUD);
>>>>>> +
>>>>>> +       return 0;
>>>>>> +}
>>>>>
>>>>> You still need to define these functions but you can make their
>>>>> implementation dependent solely on the KVM_PREALLOC_LEVEL rather than
>>>>> 64K/4K and levels combinations. If it is KVM_PREALLOC_LEVEL is 1, you
>>>>> allocate pud and populate the pgds (in a loop based on the
>>>>> PTRS_PER_S2_PGD). If it is 2, you allocate the pmd and populate the pud
>>>>> (still in a loop though it would probably be 1 iteration). We know based
>>>>> on the assumption above that you can't get KVM_PREALLOC_LEVEL == 2 and
>>>>> CONFIG_ARM64_PGTABLE_LEVELS == 4.
>>>>>
>>>>
>>>> Also agreed. Most of what you wrote here could also be gathered as
>>>> comments in the patch.
>>>>
>>> Yes, I reworded some of the text slightly as comments for the next
>>> version of the patch.
>>>
>>> However, I'm not sure I have a clear idea of how you'd like these
>>> functions to look like.
>>>
>>> I came up with the following based on your feedback, but I personally
>>> don't find it a lot easier to read than what I had already.  Suggestions
>>> are welcome:
>>>
>>> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
>>> index a030d16..7941a51 100644
>>> --- a/arch/arm64/include/asm/kvm_mmu.h
>>> +++ b/arch/arm64/include/asm/kvm_mmu.h
>>> @@ -41,6 +41,18 @@
>>>   */
>>>  #define TRAMPOLINE_VA          (HYP_PAGE_OFFSET_MASK & PAGE_MASK)
>>>
>>> +/*
>>> + * KVM_MMU_CACHE_MIN_PAGES is the number of stage2 page table translation
>>> + * levels in addition to the PGD and potentially the PUD which are
>>> + * pre-allocated (we pre-allocate the fake PGD and the PUD when the Stage-2
>>> + * tables use one level of tables less than the kernel.
>>> + */
>>> +#ifdef CONFIG_ARM64_64K_PAGES
>>> +#define KVM_MMU_CACHE_MIN_PAGES        1
>>> +#else
>>> +#define KVM_MMU_CACHE_MIN_PAGES        2
>>> +#endif
>>> +
>>>  #ifdef __ASSEMBLY__
>>>
>>>  /*
>>> @@ -53,6 +65,7 @@
>>>
>>>  #else
>>>
>>> +#include <asm/pgalloc.h>
>>>  #include <asm/cachetype.h>
>>>  #include <asm/cacheflush.h>
>>>
>>> @@ -65,10 +78,6 @@
>>>  #define KVM_PHYS_SIZE  (1UL << KVM_PHYS_SHIFT)
>>>  #define KVM_PHYS_MASK  (KVM_PHYS_SIZE - 1UL)
>>>
>>> -/* Make sure we get the right size, and thus the right alignment */
>>> -#define PTRS_PER_S2_PGD (1 << (KVM_PHYS_SHIFT - PGDIR_SHIFT))
>>> -#define S2_PGD_ORDER   get_order(PTRS_PER_S2_PGD * sizeof(pgd_t))
>>> -
>>>  int create_hyp_mappings(void *from, void *to);
>>>  int create_hyp_io_mappings(void *from, void *to, phys_addr_t);
>>>  void free_boot_hyp_pgd(void);
>>> @@ -93,6 +102,7 @@ void kvm_clear_hyp_idmap(void);
>>>  #define        kvm_set_pmd(pmdp, pmd)          set_pmd(pmdp, pmd)
>>>
>>>  static inline void kvm_clean_pgd(pgd_t *pgd) {}
>>> +static inline void kvm_clean_pmd(pmd_t *pmd) {}
>>>  static inline void kvm_clean_pmd_entry(pmd_t *pmd) {}
>>>  static inline void kvm_clean_pte(pte_t *pte) {}
>>>  static inline void kvm_clean_pte_entry(pte_t *pte) {}
>>> @@ -118,13 +128,115 @@ static inline bool kvm_page_empty(void *ptr)
>>>  }
>>>
>>>  #define kvm_pte_table_empty(ptep) kvm_page_empty(ptep)
>>> -#ifndef CONFIG_ARM64_64K_PAGES
>>> -#define kvm_pmd_table_empty(pmdp) kvm_page_empty(pmdp)
>>> -#else
>>> +
>>> +#ifdef __PAGETABLE_PMD_FOLDED
>>>  #define kvm_pmd_table_empty(pmdp) (0)
>>> +#else
>>> +#define kvm_pmd_table_empty(pmdp) kvm_page_empty(pmdp)
>>>  #endif
>>> +
>>> +#ifdef __PAGETABLE_PUD_FOLDED
>>>  #define kvm_pud_table_empty(pudp) (0)
>>> +#else
>>> +#define kvm_pud_table_empty(pudp) kvm_page_empty(pudp)
>>> +#endif
>>> +
>>> +/*
>>> + * In the case where PGDIR_SHIFT is larger than KVM_PHYS_SHIFT, we can address
>>> + * the entire IPA input range with a single pgd entry, and we would only need
>>> + * one pgd entry.
>>> + */
>>> +#if PGDIR_SHIFT > KVM_PHYS_SHIFT
>>> +#define PTRS_PER_S2_PGD                (1)
>>> +#else
>>> +#define PTRS_PER_S2_PGD                (1 << (KVM_PHYS_SHIFT - PGDIR_SHIFT))
>>> +#endif
>>> +#define S2_PGD_ORDER           get_order(PTRS_PER_S2_PGD * sizeof(pgd_t))
>>>
>>> +/*
>>> + * If we are concatenating first level stage-2 page tables, we would have less
>>> + * than or equal to 16 pointers in the fake PGD, because that's what the
>>> + * architecture allows.  In this case, (4 - CONFIG_ARM64_PGTABLE_LEVELS)
>>> + * represents the first level for the host, and we add 1 to go to the next
>>> + * level (which uses contatenation) for the stage-2 tables.
>>> + */
>>> +#if PTRS_PER_S2_PGD <= 16
>>> +#define KVM_PREALLOC_LEVEL     (4 - CONFIG_ARM64_PGTABLE_LEVELS + 1)
>>> +#else
>>> +#define KVM_PREALLOC_LEVEL     (0)
>>> +#endif
>>> +
>>> +/**
>>> + * kvm_prealloc_hwpgd - allocate inital table for VTTBR
>>> + * @kvm:       The KVM struct pointer for the VM.
>>> + * @pgd:       The kernel pseudo pgd
>>> + *
>>> + * When the kernel uses more levels of page tables than the guest, we allocate
>>> + * a fake PGD and pre-populate it to point to the next-level page table, which
>>> + * will be the real initial page table pointed to by the VTTBR.
>>> + *
>>> + * When KVM_PREALLOC_LEVEL==2, we allocate a single page for the PMD and
>>> + * the kernel will use folded pud.  When KVM_PREALLOC_LEVEL==1, we
>>> + * allocate 2 consecutive PUD pages.
>>> + */
>>> +static inline int kvm_prealloc_hwpgd(struct kvm *kvm, pgd_t *pgd)
>>> +{
>>> +       pud_t *pud;
>>> +       pmd_t *pmd;
>>> +       unsigned int order, i;
>>> +       unsigned long hwpgd;
>>> +
>>> +       if (KVM_PREALLOC_LEVEL == 0)
>>> +               return 0;
>>> +
>>> +       order = get_order(PTRS_PER_S2_PGD);
>>
>> S2_PGD_ORDER instead? Otherwise, that doesn't seem quite right...
>>
> 
> no, S2_PGD_ORDER is always the order of the PGD (in linux
> macro-world-pgd-terms) that we allocate currently.  Of course, we could
> rework that like this:
> 
> #if PTRS_PER_S2_PGD <= 16
> #define KVM_PREALLOC_LEVEL     (4 - CONFIG_ARM64_PGTABLE_LEVELS + 1)
> #define S2_PGD_ORDER           get_order(PTRS_PER_S2_PGD)
> #else
> #define KVM_PREALLOC_LEVEL     (0)
> #define S2_PGD_ORDER           get_order(PTRS_PER_S2_PGD * sizeof(pgd_t))
> #endif

I see. Got confused by the various PGD...

> 
>>> +       hwpgd = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
>>> +       if (!hwpgd)
>>> +               return -ENOMEM;
>>> +
>>> +       if (KVM_PREALLOC_LEVEL == 1) {
>>> +               pud = (pud_t *)hwpgd;
>>> +               for (i = 0; i < PTRS_PER_S2_PGD; i++)
>>> +                       pgd_populate(NULL, pgd + i, pud + i * PTRS_PER_PUD);
>>> +       } else if (KVM_PREALLOC_LEVEL == 2) {
>>> +               pud = pud_offset(pgd, 0);
>>> +               pmd = (pmd_t *)hwpgd;
>>> +               for (i = 0; i < PTRS_PER_S2_PGD; i++)
>>> +                       pud_populate(NULL, pud + i, pmd + i * PTRS_PER_PMD);
>>> +       }
>>> +
>>> +       return 0;
>>
>> Shouldn't we return an error here instead? Or BUG()?
>>
> 
> yes, should never happen.
> 
>>> +}
>>> +
>>> +static inline void *kvm_get_hwpgd(struct kvm *kvm)
>>> +{
>>> +       pgd_t *pgd = kvm->arch.pgd;
>>> +       pud_t *pud;
>>> +       pmd_t *pmd;
>>> +
>>> +       switch (KVM_PREALLOC_LEVEL) {
>>> +       case 0:
>>> +               return pgd;
>>> +       case 1:
>>> +               pud = pud_offset(pgd, 0);
>>> +               return pud;
>>> +       case 2:
>>> +               pud = pud_offset(pgd, 0);
>>> +               pmd = pmd_offset(pud, 0);
>>> +               return pmd;
>>> +       default:
>>> +               BUG();
>>> +               return NULL;
>>> +       }
>>> +}
>>> +
>>> +static inline void kvm_free_hwpgd(struct kvm *kvm)
>>> +{
>>> +       if (KVM_PREALLOC_LEVEL > 0) {
>>> +               unsigned long hwpgd = (unsigned long)kvm_get_hwpgd(kvm);
>>> +               free_pages(hwpgd, get_order(S2_PGD_ORDER));
>>
>> Isn't the get_order() a bit wrong here? I'd expect S2_PGD_ORDER to be
>> what we need already...
>>
> 
> yikes!  gonzo coding.
> 
> what it should be is
>         free_pages(hwpgd, get_order(PTRS_PER_S2_PGD));
> 
> but it ties into the discussion above.

Agreed.

>>> +       }
>>> +}
>>
>> I personally like this version more (Catalin may have a different
>> opinion ;-).
>>
> I'm fine with this, but I wasn't sure if you guys had something more
> clever/beautiful in mind....?

See Catalin's reply, but I'm happy either way.

Thanks,

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