Re: [PATCH v2 2/2] arm64: tlb: Use the TLBI RANGE feature in arm64

Catalin Marinas
2020-07-10T18:32:08Z

On Fri, Jul 10, 2020 at 05:44:20PM +0800, Zhenyu Ye wrote:
> Add __TLBI_VADDR_RANGE macro and rewrite __flush_tlb_range().
>
> When cpu supports TLBI feature, the minimum range granularity is
> decided by 'scale', so we can not flush all pages by one instruction
> in some cases.
>
> For example, when the pages = 0xe81a, let's start 'scale' from
> maximum, and find right 'num' for each 'scale':
>
> 1. scale = 3, we can flush no pages because the minimum range is
> 2^(5*3 + 1) = 0x10000.
> 2. scale = 2, the minimum range is 2^(5*2 + 1) = 0x800, we can
> flush 0xe800 pages this time, the num = 0xe800/0x800 - 1 = 0x1c.
> Remaining pages is 0x1a;
> 3. scale = 1, the minimum range is 2^(5*1 + 1) = 0x40, no page
> can be flushed.
> 4. scale = 0, we flush the remaining 0x1a pages, the num =
> 0x1a/0x2 - 1 = 0xd.
>
> However, in most scenarios, the pages = 1 when flush_tlb_range() is
> called. Start from scale = 3 or other proper value (such as scale =
> ilog2(pages)), will incur extra overhead.
> So increase 'scale' from 0 to maximum, the flush order is exactly
> opposite to the example.
>
> Signed-off-by: Zhenyu Ye <yezhenyu2@huawei.com>
> ---
> arch/arm64/include/asm/tlbflush.h | 138 +++++++++++++++++++++++-------
> 1 file changed, 109 insertions(+), 29 deletions(-)
>
> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index 39aed2efd21b..edfec8139ef8 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -60,6 +60,31 @@
> __ta; \
> })
>
> +/*
> + * Get translation granule of the system, which is decided by
> + * PAGE_SIZE. Used by TTL.
> + * - 4KB : 1
> + * - 16KB : 2
> + * - 64KB : 3
> + */
> +#define TLBI_TTL_TG_4K 1
> +#define TLBI_TTL_TG_16K 2
> +#define TLBI_TTL_TG_64K 3
> +
> +static inline unsigned long get_trans_granule(void)
> +{
> + switch (PAGE_SIZE) {
> + case SZ_4K:
> + return TLBI_TTL_TG_4K;
> + case SZ_16K:
> + return TLBI_TTL_TG_16K;
> + case SZ_64K:
> + return TLBI_TTL_TG_64K;
> + default:
> + return 0;
> + }
> +}
> +
> /*
> * Level-based TLBI operations.
> *
> @@ -73,9 +98,6 @@
> * in asm/stage2_pgtable.h.
> */
> #define TLBI_TTL_MASK GENMASK_ULL(47, 44)
> -#define TLBI_TTL_TG_4K 1
> -#define TLBI_TTL_TG_16K 2
> -#define TLBI_TTL_TG_64K 3
>
> #define __tlbi_level(op, addr, level) do { \
> u64 arg = addr; \
> @@ -83,19 +105,7 @@
> if (cpus_have_const_cap(ARM64_HAS_ARMv8_4_TTL) && \
> level) { \
> u64 ttl = level & 3; \
> - \
> - switch (PAGE_SIZE) { \
> - case SZ_4K: \
> - ttl |= TLBI_TTL_TG_4K << 2; \
> - break; \
> - case SZ_16K: \
> - ttl |= TLBI_TTL_TG_16K << 2; \
> - break; \
> - case SZ_64K: \
> - ttl |= TLBI_TTL_TG_64K << 2; \
> - break; \
> - } \
> - \
> + ttl |= get_trans_granule() << 2; \
> arg &= ~TLBI_TTL_MASK; \
> arg |= FIELD_PREP(TLBI_TTL_MASK, ttl); \
> } \
> @@ -108,6 +118,39 @@
> __tlbi_level(op, (arg | USER_ASID_FLAG), level); \
> } while (0)
>
> +/*
> + * This macro creates a properly formatted VA operand for the TLBI RANGE.
> + * The value bit assignments are:
> + *
> + * +----------+------+-------+-------+-------+----------------------+
> + * | ASID | TG | SCALE | NUM | TTL | BADDR |
> + * +-----------------+-------+-------+-------+----------------------+
> + * |63 48|47 46|45 44|43 39|38 37|36 0|
> + *
> + * The address range is determined by below formula:
> + * [BADDR, BADDR + (NUM + 1) * 2^(5*SCALE + 1) * PAGESIZE)
> + *
> + */
> +#define __TLBI_VADDR_RANGE(addr, asid, scale, num, ttl) \
> + ({ \
> + unsigned long __ta = (addr) >> PAGE_SHIFT; \
> + __ta &= GENMASK_ULL(36, 0); \
> + __ta |= (unsigned long)(ttl & 3) << 37; \
> + __ta |= (unsigned long)(num & 31) << 39; \
> + __ta |= (unsigned long)(scale & 3) << 44; \
> + __ta |= (get_trans_granule() & 3) << 46; \
> + __ta |= (unsigned long)(asid) << 48; \
> + __ta; \
> + })

Nitpick: we don't need the additional masking here (e.g. ttl & 3) since
the values are capped anyway.

> +
> +/* These macros are used by the TLBI RANGE feature. */
> +#define __TLBI_RANGE_PAGES(num, scale) (((num) + 1) << (5 * (scale) + 1))
> +#define MAX_TLBI_RANGE_PAGES __TLBI_RANGE_PAGES(31, 3)
> +
> +#define TLBI_RANGE_MASK GENMASK_ULL(4, 0)
> +#define __TLBI_RANGE_NUM(range, scale) \
> + (((range) >> (5 * (scale) + 1)) & TLBI_RANGE_MASK)
> +
> /*
> * TLB Invalidation
> * ================
> @@ -232,32 +275,69 @@ static inline void __flush_tlb_range(struct vm_area_struct *vma,
> unsigned long stride, bool last_level,
> int tlb_level)
> {
> + int num = 0;
> + int scale = 0;
> unsigned long asid = ASID(vma->vm_mm);
> unsigned long addr;
> + unsigned long pages;
>
> start = round_down(start, stride);
> end = round_up(end, stride);
> + pages = (end - start) >> PAGE_SHIFT;
>
> - if ((end - start) >= (MAX_TLBI_OPS * stride)) {
> + if ((!cpus_have_const_cap(ARM64_HAS_TLBI_RANGE) &&
> + (end - start) >= (MAX_TLBI_OPS * stride)) ||
> + pages >= MAX_TLBI_RANGE_PAGES) {
> flush_tlb_mm(vma->vm_mm);
> return;
> }

I think we can use strictly greater here rather than greater or equal.
MAX_TLBI_RANGE_PAGES can be encoded as num 31, scale 3.

>
> - /* Convert the stride into units of 4k */
> - stride >>= 12;
> + dsb(ishst);
>
> - start = __TLBI_VADDR(start, asid);
> - end = __TLBI_VADDR(end, asid);
> + /*
> + * When cpu does not support TLBI RANGE feature, we flush the tlb
> + * entries one by one at the granularity of 'stride'.
> + * When cpu supports the TLBI RANGE feature, then:
> + * 1. If pages is odd, flush the first page through non-RANGE
> + * instruction;
> + * 2. For remaining pages: The minimum range granularity is decided
> + * by 'scale', so we can not flush all pages by one instruction
> + * in some cases.
> + * Here, we start from scale = 0, flush corresponding pages
> + * (from 2^(5*scale + 1) to 2^(5*(scale + 1) + 1)), and increase
> + * it until no pages left.
> + */
> + while (pages > 0) {

I did some simple checks on ((end - start) % stride) and never
triggered. I had a slight worry that pages could become negative (and
we'd loop forever since it's unsigned long) for some mismatched stride
and flush size. It doesn't seem like.

> + if (!cpus_have_const_cap(ARM64_HAS_TLBI_RANGE) ||
> + pages % 2 == 1) {
> + addr = __TLBI_VADDR(start, asid);
> + if (last_level) {
> + __tlbi_level(vale1is, addr, tlb_level);
> + __tlbi_user_level(vale1is, addr, tlb_level);
> + } else {
> + __tlbi_level(vae1is, addr, tlb_level);
> + __tlbi_user_level(vae1is, addr, tlb_level);
> + }
> + start += stride;
> + pages -= stride >> PAGE_SHIFT;
> + continue;
> + }
>
> - dsb(ishst);
> - for (addr = start; addr < end; addr += stride) {
> - if (last_level) {
> - __tlbi_level(vale1is, addr, tlb_level);
> - __tlbi_user_level(vale1is, addr, tlb_level);
> - } else {
> - __tlbi_level(vae1is, addr, tlb_level);
> - __tlbi_user_level(vae1is, addr, tlb_level);
> + num = __TLBI_RANGE_NUM(pages, scale) - 1;
> + if (num >= 0) {
> + addr = __TLBI_VADDR_RANGE(start, asid, scale,
> + num, tlb_level);
> + if (last_level) {
> + __tlbi(rvale1is, addr);
> + __tlbi_user(rvale1is, addr);
> + } else {
> + __tlbi(rvae1is, addr);
> + __tlbi_user(rvae1is, addr);
> + }
> + start += __TLBI_RANGE_PAGES(num, scale) << PAGE_SHIFT;
> + pages -= __TLBI_RANGE_PAGES(num, scale);
> }
> + scale++;
> }
> dsb(ish);

The logic looks fine to me now. I can fix the above nitpicks myself and
maybe adjust the comment a bit. I plan to push them into next to see if
anything explodes.

Thanks.

--
Catalin