Re: [PATCH V6 12/22] LoongArch: Add memory management

From: Huacai Chen
Date: Fri Mar 04 2022 - 05:12:52 EST

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In reply to: Mike Rapoport: "Re: [PATCH V6 12/22] LoongArch: Add memory management"
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Hi, Mike,

On Fri, Mar 4, 2022 at 12:16 AM Mike Rapoport <rppt@xxxxxxxxxx> wrote:
>
> On Sat, Feb 26, 2022 at 07:03:28PM +0800, Huacai Chen wrote:
> > This patch adds memory management support for LoongArch, including:
> > cache and tlb management, page fault handling and ioremap/mmap support.
> >
> > Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> > ---
>
> ...
>
> > diff --git a/arch/loongarch/include/asm/fixmap.h b/arch/loongarch/include/asm/fixmap.h
> > new file mode 100644
> > index 000000000000..04ac3c871294
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/fixmap.h
> > @@ -0,0 +1,15 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * fixmap.h: compile-time virtual memory allocation
> > + *
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + */
> > +
> > +#ifndef _ASM_FIXMAP_H
> > +#define _ASM_FIXMAP_H
> > +
> > +#include <asm/page.h>
>
> Why this include is needed here?
OK, let's remove it.

>
> > +
> > +#define NR_FIX_BTMAPS 64
> > +
> > +#endif
> > diff --git a/arch/loongarch/include/asm/page.h b/arch/loongarch/include/asm/page.h
> > new file mode 100644
> > index 000000000000..8619ef2823ad
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/page.h
> > @@ -0,0 +1,127 @@
>
> ...
>
> > +/*
> > + * __pa()/__va() should be used only during mem init.
> > + */
> > +#define __pa(x) PHYSADDR(x)
> > +#define __va(x) ((void *)((unsigned long)(x) + PAGE_OFFSET - PHYS_OFFSET))
> > +
> > +#ifndef __pa_symbol
> > +#define __pa_symbol(x) __pa(RELOC_HIDE((unsigned long)(x), 0))
> > +#endif
>
> This is the same definition as in include/linux/mm.h.
> Is it required here?
OK, let's remove it.

>
> ...
>
> > diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> > new file mode 100644
> > index 000000000000..61993cd4c3d7
> > --- /dev/null
> > +++ b/arch/loongarch/include/asm/pgtable.h
>
> ...
>
> > +#define PGD_ORDER 0
> > +#define PUD_ORDER 0
> > +#define PMD_ORDER 0
> > +#define PTE_ORDER 0
>
> Is it possible for these to change?
> If not, please remove them.
>
> ...
>
> > diff --git a/arch/loongarch/mm/fault.c b/arch/loongarch/mm/fault.c
> > new file mode 100644
> > index 000000000000..d0170e4d5fe0
> > --- /dev/null
> > +++ b/arch/loongarch/mm/fault.c
> > @@ -0,0 +1,257 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
> > + *
> > + * Derived from MIPS:
> > + * Copyright (C) 1995 - 2000 by Ralf Baechle
> > + */
> > +#include <linux/context_tracking.h>
> > +#include <linux/signal.h>
> > +#include <linux/sched.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/kernel.h>
> > +#include <linux/entry-common.h>
> > +#include <linux/errno.h>
> > +#include <linux/string.h>
> > +#include <linux/types.h>
> > +#include <linux/ptrace.h>
> > +#include <linux/ratelimit.h>
> > +#include <linux/mman.h>
> > +#include <linux/mm.h>
> > +#include <linux/smp.h>
> > +#include <linux/kdebug.h>
> > +#include <linux/kprobes.h>
> > +#include <linux/perf_event.h>
> > +#include <linux/uaccess.h>
> > +
> > +#include <asm/branch.h>
> > +#include <asm/mmu_context.h>
> > +#include <asm/ptrace.h>
> > +
> > +int show_unhandled_signals = 1;
> > +
> > +/*
> > + * This routine handles page faults. It determines the address,
> > + * and the problem, and then passes it off to one of the appropriate
> > + * routines.
> > + */
> > +static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
> > + unsigned long address)
> > +{
> > + int si_code;
> > + const int field = sizeof(unsigned long) * 2;
> > + unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
> > + struct task_struct *tsk = current;
> > + struct mm_struct *mm = tsk->mm;
> > + struct vm_area_struct *vma = NULL;
> > + vm_fault_t fault;
> > +
> > + static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);
> > +
> > + si_code = SEGV_MAPERR;
> > +
> > + if (user_mode(regs) && (address & __UA_LIMIT))
> > + goto bad_area_nosemaphore;
> > +
> > + /*
> > + * We fault-in kernel-space virtual memory on-demand. The
> > + * 'reference' page table is init_mm.pgd.
> > + *
> > + * NOTE! We MUST NOT take any locks for this case. We may
> > + * be in an interrupt or a critical region, and should
> > + * only copy the information from the master page table,
> > + * nothing more.
> > + */
> > + if (unlikely(address >= MODULES_VADDR && address <= MODULES_END))
> > + goto no_context;
> > +
> > + if (unlikely(address >= VMALLOC_START && address <= VMALLOC_END))
> > + goto no_context;
> > +
> > + /*
> > + * If we're in an interrupt or have no user
> > + * context, we must not take the fault..
> > + */
> > + if (faulthandler_disabled() || !mm)
> > + goto bad_area_nosemaphore;
> > +
> > + if (user_mode(regs))
> > + flags |= FAULT_FLAG_USER;
> > +retry:
> > + mmap_read_lock(mm);
> > + vma = find_vma(mm, address);
> > + if (!vma)
> > + goto bad_area;
> > + if (vma->vm_start <= address)
> > + goto good_area;
> > + if (!(vma->vm_flags & VM_GROWSDOWN))
> > + goto bad_area;
> > + if (expand_stack(vma, address))
> > + goto bad_area;
> > +/*
> > + * Ok, we have a good vm_area for this memory access, so
> > + * we can handle it..
> > + */
> > +good_area:
> > + si_code = SEGV_ACCERR;
> > +
> > + if (write) {
> > + if (!(vma->vm_flags & VM_WRITE))
> > + goto bad_area;
> > + flags |= FAULT_FLAG_WRITE;
> > + } else {
> > + if (address == regs->csr_era && !(vma->vm_flags & VM_EXEC))
> > + goto bad_area;
> > + if (!(vma->vm_flags & VM_READ) && exception_era(regs) != address)
> > + goto bad_area;
> > + }
> > +
> > + /*
> > + * If for any reason at all we couldn't handle the fault,
> > + * make sure we exit gracefully rather than endlessly redo
> > + * the fault.
> > + */
> > + fault = handle_mm_fault(vma, address, flags, regs);
> > +
> > + if (fault_signal_pending(fault, regs)) {
> > + if (!user_mode(regs))
> > + goto no_context;
> > + return;
> > + }
> > +
> > + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
> > + if (unlikely(fault & VM_FAULT_ERROR)) {
> > + if (fault & VM_FAULT_OOM)
> > + goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > + else if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE))
> > + goto do_sigbus;
> > + BUG();
> > + }
> > + if (flags & FAULT_FLAG_ALLOW_RETRY) {
> > + if (fault & VM_FAULT_MAJOR) {
> > + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
> > + regs, address);
> > + tsk->maj_flt++;
> > + } else {
> > + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
> > + regs, address);
> > + tsk->min_flt++;
> > + }
> > + if (fault & VM_FAULT_RETRY) {
> > + flags &= ~FAULT_FLAG_ALLOW_RETRY;
> > + flags |= FAULT_FLAG_TRIED;
> > +
> > + /*
> > + * No need to mmap_read_unlock(mm) as we would
> > + * have already released it in __lock_page_or_retry
> > + * in mm/filemap.c.
> > + */
> > +
> > + goto retry;
> > + }
> > + }
> > +
> > + mmap_read_unlock(mm);
> > + return;
> > +
> > +/*
> > + * Something tried to access memory that isn't in our memory map..
> > + * Fix it, but check if it's kernel or user first..
> > + */
> > +bad_area:
> > + mmap_read_unlock(mm);
> > +
> > +bad_area_nosemaphore:
> > + /* User mode accesses just cause a SIGSEGV */
> > + if (user_mode(regs)) {
> > + tsk->thread.csr_badvaddr = address;
> > + if (!write)
> > + tsk->thread.error_code = 1;
> > + else
> > + tsk->thread.error_code = 2;
> > +
> > + if (show_unhandled_signals &&
> > + unhandled_signal(tsk, SIGSEGV) &&
> > + __ratelimit(&ratelimit_state)) {
> > + pr_info("do_page_fault(): sending SIGSEGV to %s for invalid %s %0*lx\n",
> > + tsk->comm,
> > + write ? "write access to" : "read access from",
> > + field, address);
> > + pr_info("era = %0*lx in", field,
> > + (unsigned long) regs->csr_era);
> > + print_vma_addr(KERN_CONT " ", regs->csr_era);
> > + pr_cont("\n");
> > + pr_info("ra = %0*lx in", field,
> > + (unsigned long) regs->regs[1]);
> > + print_vma_addr(KERN_CONT " ", regs->regs[1]);
> > + pr_cont("\n");
> > + }
> > + current->thread.trap_nr = read_csr_excode();
> > + force_sig_fault(SIGSEGV, si_code, (void __user *)address);
> > + return;
> > + }
> > +
> > +no_context:
> > + /* Are we prepared to handle this kernel fault? */
> > + if (fixup_exception(regs))
> > + return;
> > +
> > + /*
> > + * Oops. The kernel tried to access some bad page. We'll have to
> > + * terminate things with extreme prejudice.
> > + */
> > + bust_spinlocks(1);
> > +
> > + pr_alert("CPU %d Unable to handle kernel paging request at "
> > + "virtual address %0*lx, era == %0*lx, ra == %0*lx\n",
> > + raw_smp_processor_id(), field, address, field, regs->csr_era,
> > + field, regs->regs[1]);
> > + die("Oops", regs);
> > +
> > +out_of_memory:
> > + /*
> > + * We ran out of memory, call the OOM killer, and return the userspace
> > + * (which will retry the fault, or kill us if we got oom-killed).
> > + */
> > + mmap_read_unlock(mm);
> > + if (!user_mode(regs))
> > + goto no_context;
> > + pagefault_out_of_memory();
> > +
> > + return;
> > +
> > +do_sigbus:
> > + mmap_read_unlock(mm);
> > +
> > + /* Kernel mode? Handle exceptions or die */
> > + if (!user_mode(regs))
> > + goto no_context;
> > +
> > + /*
> > + * Send a sigbus, regardless of whether we were in kernel
> > + * or user mode.
> > + */
> > + current->thread.trap_nr = read_csr_excode();
> > + tsk->thread.csr_badvaddr = address;
> > + force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
> > +
>
> The page fault handler is really long.
> Consider splitting it to several functions.
OK, it's difficult but let me try.

>
> > + return;
> > +}
> > +
> > +asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
> > + unsigned long write, unsigned long address)
> > +{
> > + irqentry_state_t state = irqentry_enter(regs);
> > +
> > + /* Enable interrupt if enabled in parent context */
> > + if (likely(regs->csr_prmd & CSR_PRMD_PIE))
> > + local_irq_enable();
> > +
> > + __do_page_fault(regs, write, address);
> > +
> > + local_irq_disable();
> > +
> > + irqentry_exit(regs, state);
> > +}
>
> ...
>
> > diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
> > new file mode 100644
> > index 000000000000..b8aa96903056
> > --- /dev/null
> > +++ b/arch/loongarch/mm/init.c
> > @@ -0,0 +1,196 @@
>
> ...
>
> > +void free_init_pages(const char *what, unsigned long begin, unsigned long end)
> > +{
>
> This function seems unused
OK, let's remove it.

>
> > + unsigned long pfn;
> > +
> > + for (pfn = PFN_UP(begin); pfn < PFN_DOWN(end); pfn++) {
> > + struct page *page = pfn_to_page(pfn);
> > + void *addr = phys_to_virt(PFN_PHYS(pfn));
> > +
> > + memset(addr, POISON_FREE_INITMEM, PAGE_SIZE);
> > + free_reserved_page(page);
> > + }
> > + pr_info("Freeing %s: %ldk freed\n", what, (end - begin) >> 10);
> > +}
> > +
> > +#ifdef CONFIG_BLK_DEV_INITRD
> > +void free_initrd_mem(unsigned long start, unsigned long end)
> > +{
>
> There is a generic free_initrd_mem(), no need to override it.
OK, let's remove it.

Huacai
>
> > + free_reserved_area((void *)start, (void *)end, POISON_FREE_INITMEM,
> > + "initrd");
> > +}
> > +#endif
>
> --
> Sincerely yours,
> Mike.

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