access_process_vm device memory infrastructure

In order to be able to debug things like the X server and programs using
the PPC Cell SPUs, the debugger needs to be able to access device memory
through ptrace and /proc/pid/mem.

This patch:

Add the generic_access_phys access function and put the hooks in place
to allow access_process_vm to access device or PPC Cell SPU memory.

[riel@redhat.com: Add documentation for the vm_ops->access function]
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Benjamin Herrensmidt <benh@kernel.crashing.org>
Cc: Dave Airlie <airlied@linux.ie>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 113 insertions, 18 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 46dbed4b7446..87350321e66f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2751,6 +2751,86 @@ int in_gate_area_no_task(unsigned long addr)
 
 #endif  /* __HAVE_ARCH_GATE_AREA */
 
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+static resource_size_t follow_phys(struct vm_area_struct *vma,
+                        unsigned long address, unsigned int flags,
+                        unsigned long *prot)
+{
+        pgd_t *pgd;
+        pud_t *pud;
+        pmd_t *pmd;
+        pte_t *ptep, pte;
+        spinlock_t *ptl;
+        resource_size_t phys_addr = 0;
+        struct mm_struct *mm = vma->vm_mm;
+
+        VM_BUG_ON(!(vma->vm_flags & (VM_IO | VM_PFNMAP)));
+
+        pgd = pgd_offset(mm, address);
+        if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+                goto no_page_table;
+
+        pud = pud_offset(pgd, address);
+        if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+                goto no_page_table;
+
+        pmd = pmd_offset(pud, address);
+        if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+                goto no_page_table;
+
+        /* We cannot handle huge page PFN maps. Luckily they don't exist. */
+        if (pmd_huge(*pmd))
+                goto no_page_table;
+
+        ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
+        if (!ptep)
+                goto out;
+
+        pte = *ptep;
+        if (!pte_present(pte))
+                goto unlock;
+        if ((flags & FOLL_WRITE) && !pte_write(pte))
+                goto unlock;
+        phys_addr = pte_pfn(pte);
+        phys_addr <<= PAGE_SHIFT; /* Shift here to avoid overflow on PAE */
+
+        *prot = pgprot_val(pte_pgprot(pte));
+
+unlock:
+        pte_unmap_unlock(ptep, ptl);
+out:
+        return phys_addr;
+no_page_table:
+        return 0;
+}
+
+int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
+                        void *buf, int len, int write)
+{
+        resource_size_t phys_addr;
+        unsigned long prot = 0;
+        void *maddr;
+        int offset = addr & (PAGE_SIZE-1);
+
+        if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+                return -EINVAL;
+
+        phys_addr = follow_phys(vma, addr, write, &prot);
+
+        if (!phys_addr)
+                return -EINVAL;
+
+        maddr = ioremap_prot(phys_addr, PAGE_SIZE, prot);
+        if (write)
+                memcpy_toio(maddr + offset, buf, len);
+        else
+                memcpy_fromio(buf, maddr + offset, len);
+        iounmap(maddr);
+
+        return len;
+}
+#endif
+
 /*
  * Access another process' address space.
  * Source/target buffer must be kernel space,
@@ -2760,7 +2840,6 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
 {
         struct mm_struct *mm;
         struct vm_area_struct *vma;
-        struct page *page;
         void *old_buf = buf;
 
         mm = get_task_mm(tsk);
@@ -2772,28 +2851,44 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
         while (len) {
                 int bytes, ret, offset;
                 void *maddr;
+                struct page *page = NULL;
 
                 ret = get_user_pages(tsk, mm, addr, 1,
                                 write, 1, &page, &vma);
-                if (ret <= 0)
-                        break;
-
-                bytes = len;
-                offset = addr & (PAGE_SIZE-1);
-                if (bytes > PAGE_SIZE-offset)
-                        bytes = PAGE_SIZE-offset;
-
-                maddr = kmap(page);
-                if (write) {
-                        copy_to_user_page(vma, page, addr,
-                                          maddr + offset, buf, bytes);
-                        set_page_dirty_lock(page);
+                if (ret <= 0) {
+                        /*
+                         * Check if this is a VM_IO | VM_PFNMAP VMA, which
+                         * we can access using slightly different code.
+                         */
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+                        vma = find_vma(mm, addr);
+                        if (!vma)
+                                break;
+                        if (vma->vm_ops && vma->vm_ops->access)
+                                ret = vma->vm_ops->access(vma, addr, buf,
+                                                          len, write);
+                        if (ret <= 0)
+#endif
+                                break;
+                        bytes = ret;
                 } else {
-                        copy_from_user_page(vma, page, addr,
-                                            buf, maddr + offset, bytes);
+                        bytes = len;
+                        offset = addr & (PAGE_SIZE-1);
+                        if (bytes > PAGE_SIZE-offset)
+                                bytes = PAGE_SIZE-offset;
+
+                        maddr = kmap(page);
+                        if (write) {
+                                copy_to_user_page(vma, page, addr,
+                                                  maddr + offset, buf, bytes);
+                                set_page_dirty_lock(page);
+                        } else {
+                                copy_from_user_page(vma, page, addr,
+                                                    buf, maddr + offset, bytes);
+                        }
+                        kunmap(page);
+                        page_cache_release(page);
                 }
-                kunmap(page);
-                page_cache_release(page);
                 len -= bytes;
                 buf += bytes;
                 addr += bytes;