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

[Mike Rapoport <rppt@kernel.org>]

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@loongson.cn>
> ---

...

> 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?

> +
> +#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?

...

> 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.

> +	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

> +	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.

> +	free_reserved_area((void *)start, (void *)end, POISON_FREE_INITMEM,
> +			   "initrd");
> +}
> +#endif

-- 
Sincerely yours,
Mike.