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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] xen/arm: guest_walk: Only generate necessary offsets/masks
On Mon, 5 Apr 2021, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> At the moment, we are computing offsets/masks for each level and
> granularity. This is a bit of waste given that we only need to
> know the offsets/masks for the granularity used by the guest.
>
> All the LPAE information can easily be inferred with just the
> page shift for a given granularity and the level.
>
> So rather than providing a set of helpers per granularity, we can
> provide a single set that takes the granularity and the level in
> parameters.
>
> With the new helpers in place, we can rework guest_walk_ld() to
> only compute necessary information.
>
> Signed-off-by: Julien Grall <julien@xxxxxxxxxx>
Very nice!!
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> ---
> xen/arch/arm/guest_walk.c | 37 ++---------------
> xen/include/asm-arm/lpae.h | 82 +++++++++++++-------------------------
> 2 files changed, 30 insertions(+), 89 deletions(-)
>
> diff --git a/xen/arch/arm/guest_walk.c b/xen/arch/arm/guest_walk.c
> index b4496c4c86c6..87de40d0cb68 100644
> --- a/xen/arch/arm/guest_walk.c
> +++ b/xen/arch/arm/guest_walk.c
> @@ -372,38 +372,6 @@ static bool guest_walk_ld(const struct vcpu *v,
> register_t tcr = READ_SYSREG(TCR_EL1);
> struct domain *d = v->domain;
>
> -#define OFFSETS(gva, gran) \
> -{ \
> - zeroeth_table_offset_##gran(gva), \
> - first_table_offset_##gran(gva), \
> - second_table_offset_##gran(gva), \
> - third_table_offset_##gran(gva) \
> -}
> -
> - const paddr_t offsets[3][4] = {
> - OFFSETS(gva, 4K),
> - OFFSETS(gva, 16K),
> - OFFSETS(gva, 64K)
> - };
> -
> -#undef OFFSETS
> -
> -#define MASKS(gran) \
> -{ \
> - zeroeth_size(gran) - 1, \
> - first_size(gran) - 1, \
> - second_size(gran) - 1, \
> - third_size(gran) - 1 \
> -}
> -
> - static const paddr_t masks[3][4] = {
> - MASKS(4K),
> - MASKS(16K),
> - MASKS(64K)
> - };
> -
> -#undef MASKS
> -
> static const unsigned int grainsizes[3] = {
> PAGE_SHIFT_4K,
> PAGE_SHIFT_16K,
> @@ -519,7 +487,7 @@ static bool guest_walk_ld(const struct vcpu *v,
> * Add offset given by the GVA to the translation table base address.
> * Shift the offset by 3 as it is 8-byte aligned.
> */
> - paddr |= offsets[gran][level] << 3;
> + paddr |= LPAE_TABLE_INDEX_GS(grainsizes[gran], level, gva) << 3;
>
> /* Access the guest's memory to read only one PTE. */
> ret = access_guest_memory_by_ipa(d, paddr, &pte, sizeof(lpae_t),
> false);
> @@ -572,7 +540,8 @@ static bool guest_walk_ld(const struct vcpu *v,
>
> /* Make sure that the lower bits of the PTE's base address are zero. */
> mask = GENMASK_ULL(47, grainsizes[gran]);
> - *ipa = (pfn_to_paddr(pte.walk.base) & mask) | (gva & masks[gran][level]);
> + *ipa = (pfn_to_paddr(pte.walk.base) & mask) |
> + (gva & (LEVEL_SIZE_GS(grainsizes[gran], level) - 1));
>
> /*
> * Set permissions so that the caller can check the flags by herself.
> Note
> diff --git a/xen/include/asm-arm/lpae.h b/xen/include/asm-arm/lpae.h
> index 4797f9cee494..e94de2e7d8e8 100644
> --- a/xen/include/asm-arm/lpae.h
> +++ b/xen/include/asm-arm/lpae.h
> @@ -160,63 +160,35 @@ static inline bool lpae_is_superpage(lpae_t pte,
> unsigned int level)
> #define lpae_set_mfn(pte, mfn) ((pte).walk.base = mfn_x(mfn))
>
> /*
> - * AArch64 supports pages with different sizes (4K, 16K, and 64K). To enable
> - * page table walks for various configurations, the following helpers enable
> - * walking the translation table with varying page size granularities.
> + * AArch64 supports pages with different sizes (4K, 16K, and 64K).
> + * Provide a set of generic helpers that will compute various
> + * information based on the page granularity.
> + *
> + * Note the parameter 'gs' is the page shift of the granularity used.
> + * Some macro will evaluate 'gs' twice rather than storing in a
> + * variable. This is to allow using the macros in assembly.
> + */
> +
> +/*
> + * Granularity | PAGE_SHIFT | LPAE_SHIFT
> + * -------------------------------------
> + * 4K | 12 | 9
> + * 16K | 14 | 11
> + * 64K | 16 | 13
> + *
> + * This is equivalent to LPAE_SHIFT = PAGE_SHIFT - 3
> */
> +#define LPAE_SHIFT_GS(gs) ((gs) - 3)
> +#define LPAE_ENTRIES_GS(gs) (_AC(1, U) << LPAE_SHIFT_GS(gs))
> +#define LPAE_ENTRIES_MASK_GS(gs) (LPAE_ENTRIES_GS(gs) - 1)
> +
> +#define LEVEL_ORDER_GS(gs, lvl) ((3 - (lvl)) * LPAE_SHIFT_GS(gs))
> +#define LEVEL_SHIFT_GS(gs, lvl) (LEVEL_ORDER_GS(gs, lvl) + (gs))
> +#define LEVEL_SIZE_GS(gs, lvl) (_AT(paddr_t, 1) << LEVEL_SHIFT_GS(gs,
> lvl))
>
> -#define LPAE_SHIFT_4K (9)
> -#define LPAE_SHIFT_16K (11)
> -#define LPAE_SHIFT_64K (13)
> -
> -#define lpae_entries(gran) (_AC(1,U) << LPAE_SHIFT_##gran)
> -#define lpae_entry_mask(gran) (lpae_entries(gran) - 1)
> -
> -#define third_shift(gran) (PAGE_SHIFT_##gran)
> -#define third_size(gran) ((paddr_t)1 << third_shift(gran))
> -
> -#define second_shift(gran) (third_shift(gran) + LPAE_SHIFT_##gran)
> -#define second_size(gran) ((paddr_t)1 << second_shift(gran))
> -
> -#define first_shift(gran) (second_shift(gran) + LPAE_SHIFT_##gran)
> -#define first_size(gran) ((paddr_t)1 << first_shift(gran))
> -
> -/* Note that there is no zeroeth lookup level with a 64K granule size. */
> -#define zeroeth_shift(gran) (first_shift(gran) + LPAE_SHIFT_##gran)
> -#define zeroeth_size(gran) ((paddr_t)1 << zeroeth_shift(gran))
> -
> -#define TABLE_OFFSET(offs, gran) (offs & lpae_entry_mask(gran))
> -#define TABLE_OFFSET_HELPERS(gran) \
> -static inline paddr_t third_table_offset_##gran##K(paddr_t va) \
> -{ \
> - return TABLE_OFFSET((va >> third_shift(gran##K)), gran##K); \
> -} \
> - \
> -static inline paddr_t second_table_offset_##gran##K(paddr_t va) \
> -{ \
> - return TABLE_OFFSET((va >> second_shift(gran##K)), gran##K); \
> -} \
> - \
> -static inline paddr_t first_table_offset_##gran##K(paddr_t va) \
> -{ \
> - return TABLE_OFFSET((va >> first_shift(gran##K)), gran##K); \
> -} \
> - \
> -static inline paddr_t zeroeth_table_offset_##gran##K(paddr_t va) \
> -{ \
> - /* Note that there is no zeroeth lookup level with 64K granule sizes. */\
> - if ( gran == 64 ) \
> - return 0; \
> - else \
> - return TABLE_OFFSET((va >> zeroeth_shift(gran##K)), gran##K); \
> -} \
> -
> -TABLE_OFFSET_HELPERS(4);
> -TABLE_OFFSET_HELPERS(16);
> -TABLE_OFFSET_HELPERS(64);
> -
> -#undef TABLE_OFFSET
> -#undef TABLE_OFFSET_HELPERS
> +/* Offset in the table at level 'lvl' */
> +#define LPAE_TABLE_INDEX_GS(gs, lvl, addr) \
> + (((addr) >> LEVEL_SHIFT_GS(gs, lvl)) & LPAE_ENTRIES_MASK_GS(gs))
>
> /* Generate an array @var containing the offset for each level from @addr */
> #define DECLARE_OFFSETS(var, addr) \
> --
> 2.17.1
>
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