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Message-ID: <f1a5ec6e-540b-497f-a9ad-f2d1e7adfc65@ghiti.fr>
Date: Sat, 20 Jun 2020 05:04:00 -0400
From: Alex Ghiti <alex@...ti.fr>
To: Atish Patra <atishp@...shpatra.org>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Anup Patel <anup@...infault.org>,
Atish Patra <Atish.Patra@....com>,
linux-riscv <linux-riscv@...ts.infradead.org>,
"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] riscv: Use PUD/PGDIR entries for linear mapping when
possible
Hi Atish,
Le 6/19/20 à 2:16 PM, Atish Patra a écrit :
> On Thu, Jun 18, 2020 at 9:28 PM Alex Ghiti <alex@...ti.fr> wrote:
>> Hi Atish,
>>
>> Le 6/18/20 à 8:47 PM, Atish Patra a écrit :
>>> On Wed, Jun 3, 2020 at 8:38 AM Alexandre Ghiti <alex@...ti.fr> wrote:
>>>> Improve best_map_size so that PUD or PGDIR entries are used for linear
>>>> mapping when possible as it allows better TLB utilization.
>>>>
>>>> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
>>>> ---
>>>> arch/riscv/mm/init.c | 45 +++++++++++++++++++++++++++++++++-----------
>>>> 1 file changed, 34 insertions(+), 11 deletions(-)
>>>>
>>>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>>>> index 9a5c97e091c1..d275f9f834cf 100644
>>>> --- a/arch/riscv/mm/init.c
>>>> +++ b/arch/riscv/mm/init.c
>>>> @@ -424,13 +424,29 @@ static void __init create_pgd_mapping(pgd_t *pgdp,
>>>> create_pgd_next_mapping(nextp, va, pa, sz, prot);
>>>> }
>>>>
>>>> -static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
>>>> +static bool is_map_size_ok(uintptr_t map_size, phys_addr_t base,
>>>> + uintptr_t base_virt, phys_addr_t size)
>>>> {
>>>> - /* Upgrade to PMD_SIZE mappings whenever possible */
>>>> - if ((base & (PMD_SIZE - 1)) || (size & (PMD_SIZE - 1)))
>>>> - return PAGE_SIZE;
>>>> + return !((base & (map_size - 1)) || (base_virt & (map_size - 1)) ||
>>>> + (size < map_size));
>>>> +}
>>>> +
>>>> +static uintptr_t __init best_map_size(phys_addr_t base, uintptr_t base_virt,
>>>> + phys_addr_t size)
>>>> +{
>>>> +#ifndef __PAGETABLE_PMD_FOLDED
>>>> + if (is_map_size_ok(PGDIR_SIZE, base, base_virt, size))
>>>> + return PGDIR_SIZE;
>>>> +
>>>> + if (pgtable_l4_enabled)
>>>> + if (is_map_size_ok(PUD_SIZE, base, base_virt, size))
>>>> + return PUD_SIZE;
>>>> +#endif
>>>> +
>>>> + if (is_map_size_ok(PMD_SIZE, base, base_virt, size))
>>>> + return PMD_SIZE;
>>>>
>>>> - return PMD_SIZE;
>>>> + return PAGE_SIZE;
>>>> }
>>>>
>>>> /*
>>>> @@ -576,7 +592,7 @@ void create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
>>>> asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>> {
>>>> uintptr_t va, end_va;
>>>> - uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
>>>> + uintptr_t map_size;
>>>>
>>>> load_pa = (uintptr_t)(&_start);
>>>> load_sz = (uintptr_t)(&_end) - load_pa;
>>>> @@ -587,6 +603,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>>
>>>> kernel_virt_addr = KERNEL_VIRT_ADDR;
>>>>
>>>> + map_size = best_map_size(load_pa, PAGE_OFFSET, MAX_EARLY_MAPPING_SIZE);
>>>> va_pa_offset = PAGE_OFFSET - load_pa;
>>>> va_kernel_pa_offset = kernel_virt_addr - load_pa;
>>>> pfn_base = PFN_DOWN(load_pa);
>>>> @@ -700,6 +717,8 @@ static void __init setup_vm_final(void)
>>>>
>>>> /* Map all memory banks */
>>>> for_each_memblock(memory, reg) {
>>>> + uintptr_t remaining_size;
>>>> +
>>>> start = reg->base;
>>>> end = start + reg->size;
>>>>
>>>> @@ -707,15 +726,19 @@ static void __init setup_vm_final(void)
>>>> break;
>>>> if (memblock_is_nomap(reg))
>>>> continue;
>>>> - if (start <= __pa(PAGE_OFFSET) &&
>>>> - __pa(PAGE_OFFSET) < end)
>>>> - start = __pa(PAGE_OFFSET);
>>>>
>>>> - map_size = best_map_size(start, end - start);
>>>> - for (pa = start; pa < end; pa += map_size) {
>>>> + pa = start;
>>>> + remaining_size = reg->size;
>>>> +
>>>> + while (remaining_size) {
>>>> va = (uintptr_t)__va(pa);
>>>> + map_size = best_map_size(pa, va, remaining_size);
>>>> +
>>>> create_pgd_mapping(swapper_pg_dir, va, pa,
>>>> map_size, PAGE_KERNEL);
>>>> +
>>>> + pa += map_size;
>>>> + remaining_size -= map_size;
>>>> }
>>>> }
>>>>
>>> This may not work in the RV32 with 2G memory and if the map_size is
>>> determined to be a page size
>>> for the last memblock. Both pa & remaining_size will overflow and the
>>> loop will try to map memory from zero again.
>> I'm not sure I understand: if pa starts at 0x8000_0000 and size is 2G,
>> then pa will overflow in the last iteration, but remaining_size will
>> then be equal to 0 right ?
>>
> Not unless the remaining_size is at least page size aligned. The last
> remaining size would "fff".
> It will overflow as well after subtracting the map_size.
>
>> And by the way, I realize that this loop only handles sizes that are
>> aligned on map_size.
>>
> Yeah.
Thanks for noticing, I send a v2.
Alex
>
>> Thanks,
>>
>> Alex
>>
>>
>>>> --
>>>> 2.20.1
>>>>
>>>>
>
>
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