Re: [RFC v6 04/10] PCI: Add support for enforcing all MMIO BARs to be page aligned

From: Alexey Kardashevskiy
Date: Tue Apr 26 2016 - 01:41:28 EST

On 04/18/2016 08:56 PM, Yongji Xie wrote:
When vfio passthrough a PCI device of which MMIO BARs are
smaller than PAGE_SIZE, guest will not handle the mmio
accesses to the BARs which leads to mmio emulations in host.

This is because vfio will not allow to passthrough one BAR's
mmio page which may be shared with other BARs. Otherwise,
there will be a backdoor that guest can use to access BARs
of other guest.

To solve this issue, this patch modifies resource_alignment
to support syntax where multiple devices get the same
alignment. So we can use something like
"pci=resource_alignment=*:*:*.*:noresize" to enforce the
alignment of all MMIO BARs to be at least PAGE_SIZE so that
one BAR's mmio page would not be shared with other BARs.

And we also define a macro PCIBIOS_MIN_ALIGNMENT to enable this
automatically on PPC64 platform which can easily hit this issue
because its PAGE_SIZE is 64KB.

Signed-off-by: Yongji Xie <xyjxie@xxxxxxxxxxxxxxxxxx>
---
Documentation/kernel-parameters.txt | 2 ++
arch/powerpc/include/asm/pci.h | 2 ++
drivers/pci/pci.c | 64 +++++++++++++++++++++++++++++------
3 files changed, 57 insertions(+), 11 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index d8b29ab..542be4a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2918,6 +2918,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
aligned memory resources.
If <order of align> is not specified,
PAGE_SIZE is used as alignment.
+ <domain>, <bus>, <slot> and <func> can be set to
+ "*" which means match all values.
PCI-PCI bridge can be specified, if resource
windows need to be expanded.
noresize: Don't change the resources' sizes when
diff --git a/arch/powerpc/include/asm/pci.h b/arch/powerpc/include/asm/pci.h
index 6f8065a..78f230f 100644
--- a/arch/powerpc/include/asm/pci.h
+++ b/arch/powerpc/include/asm/pci.h
@@ -30,6 +30,8 @@
#define PCIBIOS_MIN_IO 0x1000
#define PCIBIOS_MIN_MEM 0x10000000

+#define PCIBIOS_MIN_ALIGNMENT PAGE_SIZE
+
struct pci_dev;

/* Values for the `which' argument to sys_pciconfig_iobase syscall. */
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 7564ccc..0381c28 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4605,7 +4605,12 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
int seg, bus, slot, func, align_order, count;
resource_size_t align = 0;
char *p;
+ bool invalid = false;

+#ifdef PCIBIOS_MIN_ALIGNMENT
+ align = PCIBIOS_MIN_ALIGNMENT;
+ *resize = false;
+#endif
spin_lock(&resource_alignment_lock);
p = resource_alignment_param;
while (*p) {
@@ -4622,16 +4627,49 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
} else {
align_order = -1;
}
- if (sscanf(p, "%x:%x:%x.%x%n",
- &seg, &bus, &slot, &func, &count) != 4) {


I'd replace the above lines with:

char segstr[5] = "*", busstr[3] = "*";
char slotstr[3] = "*", funstr[2] = "*";

if (sscanf(p, "%4[^:]:%2[^:]:%2[^.].%1s%n",
&segstr, &busstr, &slotstr, &funcstr, &count) != 4) {


and add some wrapper like:

static bool glob_match_hex(char const *pat, int val)
{
char valstr[5]; /* 5 should be enough for PCI */
snprintf(valstr, sizeof(valstr) - 1, "%4x", val);
return glob_match(pat, valstr);
}

and then use glob_match_hex() (or make a wrapper like above on top of fnmatch()), this would enable better mask handling.

If anyone finds this useful (which I am not sure about).




+ if (p[0] == '*' && p[1] == ':') {
+ seg = -1;
+ count = 1;
+ } else if (sscanf(p, "%x%n", &seg, &count) != 1 ||
+ p[count] != ':') {
+ invalid = true;
+ break;
+ }
+ p += count + 1;
+ if (*p == '*') {
+ bus = -1;
+ count = 1;
+ } else if (sscanf(p, "%x%n", &bus, &count) != 1) {
+ invalid = true;
+ break;
+ }
+ p += count;
+ if (*p == '.') {
+ slot = bus;
+ bus = seg;
seg = 0;
- if (sscanf(p, "%x:%x.%x%n",
- &bus, &slot, &func, &count) != 3) {
- /* Invalid format */
- printk(KERN_ERR "PCI: Can't parse resource_alignment parameter: %s\n",
- p);
+ p++;
+ } else if (*p == ':') {
+ p++;
+ if (p[0] == '*' && p[1] == '.') {
+ slot = -1;
+ count = 1;
+ } else if (sscanf(p, "%x%n", &slot, &count) != 1 ||
+ p[count] != '.') {
+ invalid = true;
break;
}
+ p += count + 1;
+ } else {
+ invalid = true;
+ break;
+ }
+ if (*p == '*') {
+ func = -1;
+ count = 1;
+ } else if (sscanf(p, "%x%n", &func, &count) != 1) {
+ invalid = true;
+ break;
}
p += count;
if (!strncmp(p, ":noresize", 9)) {
@@ -4639,10 +4677,10 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
p += 9;
} else
*resize = true;
- if (seg == pci_domain_nr(dev->bus) &&
- bus == dev->bus->number &&
- slot == PCI_SLOT(dev->devfn) &&
- func == PCI_FUNC(dev->devfn)) {
+ if ((seg == pci_domain_nr(dev->bus) || seg == -1) &&
+ (bus == dev->bus->number || bus == -1) &&
+ (slot == PCI_SLOT(dev->devfn) || slot == -1) &&
+ (func == PCI_FUNC(dev->devfn) || func == -1)) {
if (align_order == -1)
align = PAGE_SIZE;
else
@@ -4652,10 +4690,14 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
}
if (*p != ';' && *p != ',') {
/* End of param or invalid format */
+ invalid = true;
break;
}
p++;
}
+ if (invalid)
+ printk(KERN_ERR "PCI: Can't parse resource_alignment parameter:%s\n",
+ p);
spin_unlock(&resource_alignment_lock);
return align;
}



--
Alexey