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kernel/resource: clean up and optimize iomem_is_exclusive()

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Patch series "virtio-mem: disallow mapping virtio-mem memory via /dev/mem", v5.

Let's add the basic infrastructure to exclude some physical memory regions
marked as "IORESOURCE_SYSTEM_RAM" completely from /dev/mem access, even
though they are not marked IORESOURCE_BUSY and even though "iomem=relaxed"
is set.  Resource IORESOURCE_EXCLUSIVE for that purpose instead of adding
new flags to express something similar to "soft-busy" or "not busy yet,
but already prepared by a driver and not to be mapped by user space".

Use it for virtio-mem, to disallow mapping any virtio-mem memory via
/dev/mem to user space after the virtio-mem driver was loaded.

This patch (of 3):

We end up traversing subtrees of ranges we are not interested in; let's
optimize this case, skipping such subtrees, cleaning up the function a
bit.

For example, in the following configuration (/proc/iomem):

  00000000-00000fff : Reserved
  00001000-00057fff : System RAM
  00058000-00058fff : Reserved
  00059000-0009cfff : System RAM
  0009d000-000fffff : Reserved
     000a0000-000bffff : PCI Bus 0000:00
     000c0000-000c3fff : PCI Bus 0000:00
     000c4000-000c7fff : PCI Bus 0000:00
     000c8000-000cbfff : PCI Bus 0000:00
     000cc000-000cffff : PCI Bus 0000:00
     000d0000-000d3fff : PCI Bus 0000:00
     000d4000-000d7fff : PCI Bus 0000:00
     000d8000-000dbfff : PCI Bus 0000:00
     000dc000-000dffff : PCI Bus 0000:00
     000e0000-000e3fff : PCI Bus 0000:00
     000e4000-000e7fff : PCI Bus 0000:00
     000e8000-000ebfff : PCI Bus 0000:00
     000ec000-000effff : PCI Bus 0000:00
     000f0000-000fffff : PCI Bus 0000:00
       000f0000-000fffff : System ROM
  00100000-3fffffff : System RAM
  40000000-403fffff : Reserved
     40000000-403fffff : pnp 00:00
  40400000-80a79fff : System RAM
  ...

We don't have to look at any children of "0009d000-000fffff : Reserved"
if we can just skip these 15 items directly because the parent range is
not of interest.

Link: https://lkml.kernel.org/r/20210920142856.17758-1-david@redhat.com
Link: https://lkml.kernel.org/r/20210920142856.17758-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2021-11-08 18:35:46 -08:00 • committed by Linus Torvalds
parent 3b2941188e
commit b78dfa059f
1 changed files with 20 additions and 5 deletions
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25
kernel/resource.c
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@ -73,6 +73,18 @@ static struct resource *next_resource(struct resource *p)
return p->sibling;
}
static struct resource *next_resource_skip_children(struct resource *p)
{
while (!p->sibling && p->parent)
p = p->parent;
return p->sibling;
}
#define for_each_resource(_root, _p, _skip_children) \
for ((_p) = (_root)->child; (_p); \
(_p) = (_skip_children) ? next_resource_skip_children(_p) : \
next_resource(_p))
static void *r_next(struct seq_file *m, void *v, loff_t *pos)
{
struct resource *p = v;
@ -1712,10 +1724,9 @@ static int strict_iomem_checks;
*/
bool iomem_is_exclusive(u64 addr)
{
struct resource *p = &iomem_resource;
bool err = false;
loff_t l;
bool skip_children = false, err = false;
int size = PAGE_SIZE;
struct resource *p;
if (!strict_iomem_checks)
return false;
@ -1723,15 +1734,19 @@ bool iomem_is_exclusive(u64 addr)
addr = addr & PAGE_MASK;
read_lock(&resource_lock);
for (p = p->child; p ; p = r_next(NULL, p, &l)) {
for_each_resource(&iomem_resource, p, skip_children) {
/*
* We can probably skip the resources without
* IORESOURCE_IO attribute?
*/
if (p->start >= addr + size)
break;
if (p->end < addr)
if (p->end < addr) {
skip_children = true;
continue;
}
skip_children = false;
/*
* A resource is exclusive if IORESOURCE_EXCLUSIVE is set
* or CONFIG_IO_STRICT_DEVMEM is enabled and the