Re: [RFC PATCH 2/5] RISC-V: Use Linux logical cpu number instead of hartid

[Atish Patra <atish.patra@wdc.com>]

On 8/15/18 10:45 PM, Anup Patel wrote:
> On Thu, Aug 16, 2018 at 10:53 AM, Atish Patra <atish.patra@wdc.com> wrote:
>> On 8/15/18 9:24 PM, Anup Patel wrote:
>>>
>>> On Thu, Aug 16, 2018 at 5:26 AM, Atish Patra <atish.patra@wdc.com> wrote:
>>>>
>>>> Setup the cpu_logical_map during boot. Moreover, every SBI call
>>>> and PLIC context are based on the physical hartid. Use the logical
>>>> cpu to hartid mapping to pass correct hartid to respective functions.
>>>>
>>>> Signed-off-by: Atish Patra <atish.patra@wdc.com>
>>>> ---
>>>>    arch/riscv/include/asm/tlbflush.h | 17 +++++++++++++----
>>>>    arch/riscv/kernel/cpu.c           |  4 +++-
>>>>    arch/riscv/kernel/setup.c         | 10 ++++++++++
>>>>    arch/riscv/kernel/smp.c           | 24 +++++++++++++++---------
>>>>    arch/riscv/kernel/smpboot.c       | 30 ++++++++++++++++++------------
>>>>    drivers/clocksource/riscv_timer.c | 12 ++++++++----
>>>>    drivers/irqchip/irq-sifive-plic.c | 11 +++++++----
>>>>    7 files changed, 74 insertions(+), 34 deletions(-)
>>>>
>>>> diff --git a/arch/riscv/include/asm/tlbflush.h
>>>> b/arch/riscv/include/asm/tlbflush.h
>>>> index 85c2d8ba..ecfd9b0e 100644
>>>> --- a/arch/riscv/include/asm/tlbflush.h
>>>> +++ b/arch/riscv/include/asm/tlbflush.h
>>>> @@ -16,6 +16,7 @@
>>>>    #define _ASM_RISCV_TLBFLUSH_H
>>>>
>>>>    #include <linux/mm_types.h>
>>>> +#include <asm/smp.h>
>>>>
>>>>    /*
>>>>     * Flush entire local TLB.  'sfence.vma' implicitly fences with the
>>>> instruction
>>>> @@ -49,13 +50,21 @@ static inline void flush_tlb_range(struct
>>>> vm_area_struct *vma,
>>>>
>>>>    #include <asm/sbi.h>
>>>>
>>>> -#define flush_tlb_all() sbi_remote_sfence_vma(NULL, 0, -1)
>>>> +static inline void remote_sfence_vma(struct cpumask *cmask, unsigned
>>>> long start,
>>>> +                                    unsigned long size)
>>>> +{
>>>> +       struct cpumask hmask;
>>>> +
>>>> +       cpuid_to_hartid_mask(cmask, &hmask);
>>>> +       sbi_remote_sfence_vma(hmask.bits, start, size);
>>>> +}
>>>> +
>>>> +#define flush_tlb_all() remote_sfence_vma(NULL, 0, -1)
>>>>    #define flush_tlb_page(vma, addr) flush_tlb_range(vma, addr, 0)
>>>>    #define flush_tlb_range(vma, start, end) \
>>>> -       sbi_remote_sfence_vma(mm_cpumask((vma)->vm_mm)->bits, \
>>>> -                             start, (end) - (start))
>>>> +       remote_sfence_vma(mm_cpumask((vma)->vm_mm), start, (end) -
>>>> (start))
>>>>    #define flush_tlb_mm(mm) \
>>>> -       sbi_remote_sfence_vma(mm_cpumask(mm)->bits, 0, -1)
>>>> +       remote_sfence_vma(mm_cpumask(mm), 0, -1)
>>>>
>>>>    #endif /* CONFIG_SMP */
>>>>
>>>> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
>>>> index ca6c81e5..f8a18ace 100644
>>>> --- a/arch/riscv/kernel/cpu.c
>>>> +++ b/arch/riscv/kernel/cpu.c
>>>> @@ -14,6 +14,7 @@
>>>>    #include <linux/init.h>
>>>>    #include <linux/seq_file.h>
>>>>    #include <linux/of.h>
>>>> +#include <asm/smp.h>
>>>>
>>>>    /* Return -1 if not a valid hart */
>>>>    int riscv_of_processor_hart(struct device_node *node)
>>>> @@ -79,7 +80,8 @@ static void c_stop(struct seq_file *m, void *v)
>>>>    static int c_show(struct seq_file *m, void *v)
>>>>    {
>>>>           unsigned long hart_id = (unsigned long)v - 1;
>>>> -       struct device_node *node = of_get_cpu_node(hart_id, NULL);
>>>> +       struct device_node *node =
>>>> of_get_cpu_node(cpu_logical_map(hart_id),
>>>> +                                                  NULL);
>>>
>>>
>>> The hart_id is misleading name here. It should be cpu_id. Please replace
>>> all instances of hart_id with cpu_id and where hard ID is to be displayed
>>> use cpu_logical_map(cpu_id).
>>>
>> Correct. Thanks for catching it. I will fix it in v2.
>>
>>
>>>>           const char *compat, *isa, *mmu;
>>>>
>>>>           seq_printf(m, "hart\t: %lu\n", hart_id);
>>>> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
>>>> index e21ed481..97b586f8 100644
>>>> --- a/arch/riscv/kernel/setup.c
>>>> +++ b/arch/riscv/kernel/setup.c
>>>> @@ -84,6 +84,16 @@ atomic_t hart_lottery;
>>>>
>>>>    u64 __cpu_logical_map[NR_CPUS];
>>>>
>>>> +void __init smp_setup_processor_id(void)
>>>> +{
>>>> +       int cpu = smp_processor_id();
>>>> +
>>>> +       cpu_logical_map(0) = cpu;
>>>
>>>
>>> I think this should be:
>>> cpu_logical_map(cpu) = hart_id;
>>>
>>> Here hart_id for boot CPU will be value of a0 register passed at
>>> boot-time.
>>>
>> I will change the variable name to hart_id. The assembly code in head.S have
>> already stored hart id in thread info structure. So smp_processor_id() and
>> hart id would be the same.
>>
>>
> 
> I guess this means that for boot CPU, cpuid == hartid
> 

No. I set the cpuid 0 for boot cpu by doing this.

+	/* Change the boot cpu ID in thread_info */
+	current->thread_info.cpu = 0;

> This is very confusing because other places I see CPU0 is the boot CPU.
> 

CPU0 is the boot cpu.
> I think assembly code in head.S should store 0 in thread info for boot CPU.
> 
If we do that, we loose track of boot cpu hartid. We have to store it 
somewhere else to update the cpu_logical_map(0). Isn't it ?

Regards,
Atish
> Regards,
> Anup
>