[regression] Re: [PATCH v6 06/12] mm/gup: track FOLL_PIN pages

From: Alex Williamson
Date: Fri Apr 24 2020 - 14:19:15 EST

On Mon, 10 Feb 2020 16:15:30 -0800
John Hubbard <jhubbard@xxxxxxxxxx> wrote:

> Add tracking of pages that were pinned via FOLL_PIN. This tracking is
> implemented via overloading of page->_refcount: pins are added by
> adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a
> fuzzy indication of pinning, and it can have false positives (and that's
> OK). Please see the pre-existing
> Documentation/core-api/pin_user_pages.rst for details.
>
> As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN
> (typically via pin_user_pages*()) are required to ultimately free such
> pages via unpin_user_page().
>
> Please also note the limitation, discussed in pin_user_pages.rst under
> the "TODO: for 1GB and larger huge pages" section. (That limitation will
> be removed in a following patch.)
>
> The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be
> thought of as "FOLL_GET for DIO and/or RDMA use".
>
> Pages that have been pinned via FOLL_PIN are identifiable via a
> new function call:
>
> bool page_maybe_dma_pinned(struct page *page);
>
> What to do in response to encountering such a page, is left to later
> patchsets. There is discussion about this in [1], [2], [3], and [4].
>
> This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask().
>
> [1] Some slow progress on get_user_pages() (Apr 2, 2019):
> https://lwn.net/Articles/784574/
> [2] DMA and get_user_pages() (LPC: Dec 12, 2018):
> https://lwn.net/Articles/774411/
> [3] The trouble with get_user_pages() (Apr 30, 2018):
> https://lwn.net/Articles/753027/
> [4] LWN kernel index: get_user_pages():
> https://lwn.net/Kernel/Index/#Memory_management-get_user_pages
>
> Reviewed-by: Jan Kara <jack@xxxxxxx>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Suggested-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
> Documentation/core-api/pin_user_pages.rst | 6 +-
> include/linux/mm.h | 82 +++++--
> mm/gup.c | 254 +++++++++++++++++-----
> mm/huge_memory.c | 29 ++-
> mm/hugetlb.c | 54 +++--
> 5 files changed, 334 insertions(+), 91 deletions(-)

Hi John,

I'm seeing a regression bisected back to this commit (3faa52c03f44
mm/gup: track FOLL_PIN pages). I've attached some vfio-pci test code
that reproduces this by mmap'ing a page of MMIO space of a device and
then tries to map that through the IOMMU, so this should be attempting
a gup/pin of a PFNMAP page. Previously this failed gracefully (-EFAULT),
but now results in:

BUG: unable to handle page fault for address: ffffae5cbfe5e938
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] SMP NOPTI
CPU: 18 PID: 3365 Comm: vfio-pci-dma-ma Tainted: G OE 5.6.0+ #6
Hardware name: AMD Corporation Diesel/Diesel, BIOS TDL100CB 03/17/2020
RIP: 0010:get_pfnblock_flags_mask+0x22/0x70
Code: c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 48 8b 05 bc e1 d9 01 48 89 f7 49 89 c8 48 c1 ef 0f 48 85 c0 74 48 48 89 f1 48 c1 e9 17 <48> 8b 04 c8 48 85 c0 74 0b 40 0f b6 ff 48 c1 e7 04 48 01 f8 48 c1
RSP: 0018:ffffb55289b3fcc8 EFLAGS: 00010216
RAX: ffff9e5cbff50000 RBX: 0000000000000001 RCX: 000001fffffe1d27
RDX: 0000000000000002 RSI: ffffff0e93acd633 RDI: 0001fffffe1d2759
RBP: ffffb55289b3fd88 R08: 0000000000000007 R09: ffff9e48a52476a8
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000001 R15: ffff9e48ab358cc0
FS: 00007f4ef7269740(0000) GS:ffff9e48afa80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffae5cbfe5e938 CR3: 0000000c61eda000 CR4: 00000000003406e0
Call Trace:
__gup_longterm_locked+0x274/0x620
vaddr_get_pfn+0x74/0x110 [vfio_iommu_type1]
vfio_pin_pages_remote+0x6e/0x370 [vfio_iommu_type1]
vfio_iommu_type1_ioctl+0x8e5/0xaac [vfio_iommu_type1]
ksys_ioctl+0x86/0xc0
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x5b/0x1f0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f4ef6d7d307
Code: 44 00 00 48 8b 05 69 1b 2d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 39 1b 2d 00 f7 d8 64 89 01 48
RSP: 002b:00007fff76ada738 EFLAGS: 00000213 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4ef6d7d307
RDX: 00007fff76ada760 RSI: 0000000000003b71 RDI: 0000000000000003
RBP: 00007fff76ada930 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000213 R12: 0000000000400950
R13: 00007fff76adaa10 R14: 0000000000000000 R15: 0000000000000000
Modules linked in: vfio_pci(OE) vfio_virqfd(OE) vfio_iommu_type1(OE) vfio(OE) amd64_edac_mod edac_mce_amd kvm_amd kvm rfkill sunrpc ipmi_ssif vfat irqbypass fat ipmi_si crct10dif_pclmul crc32_pclmul sp5100_tco ghash_clmulni_intel ipmi_devintf pcspkr joydev ccp i2c_piix4 k10temp ipmi_msghandler pinctrl_amd acpi_cpufreq ip_tables nouveau ast video mxm_wmi drm_vram_helper wmi drm_ttm_helper i2c_algo_bit drm_kms_helper cec ttm drm i40e e1000e crc32c_intel
CR2: ffffae5cbfe5e938
---[ end trace a384ab7cc8e37d46 ]---
RIP: 0010:get_pfnblock_flags_mask+0x22/0x70
Code: c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 48 8b 05 bc e1 d9 01 48 89 f7 49 89 c8 48 c1 ef 0f 48 85 c0 74 48 48 89 f1 48 c1 e9 17 <48> 8b 04 c8 48 85 c0 74 0b 40 0f b6 ff 48 c1 e7 04 48 01 f8 48 c1
RSP: 0018:ffffb55289b3fcc8 EFLAGS: 00010216
RAX: ffff9e5cbff50000 RBX: 0000000000000001 RCX: 000001fffffe1d27
RDX: 0000000000000002 RSI: ffffff0e93acd633 RDI: 0001fffffe1d2759
RBP: ffffb55289b3fd88 R08: 0000000000000007 R09: ffff9e48a52476a8
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000001 R15: ffff9e48ab358cc0
FS: 00007f4ef7269740(0000) GS:ffff9e48afa80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffae5cbfe5e938 CR3: 0000000c61eda000 CR4: 00000000003406e0

Thanks,
Alex
#include <errno.h>
#include <libgen.h>
#include <fcntl.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/eventfd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>

#include <linux/ioctl.h>
#include <linux/vfio.h>
#include <linux/pci_regs.h>

void usage(char *name)
{
fprintf(stderr, "usage: %s <ssss:bb:dd.f>\n", name);
fprintf(stderr, "\tssss: PCI segment, ex. 0000\n");
fprintf(stderr, "\tbb: PCI bus, ex. 01\n");
fprintf(stderr, "\tdd: PCI device, ex. 06\n");
fprintf(stderr, "\tf: PCI function, ex. 0\n");
}

int main(int argc, char **argv)
{
int seg, bus, slot, func;
int ret, container, group, device, groupid;
char path[50], iommu_group_path[50], *group_name;
struct stat st;
ssize_t len;
void *map = MAP_FAILED;
int i;
unsigned int bar;
struct vfio_group_status group_status = {
.argsz = sizeof(group_status)
};
struct vfio_region_info region_info = {
.argsz = sizeof(region_info)
};
struct vfio_region_info config_info = {
.argsz = sizeof(config_info)
};
struct vfio_iommu_type1_dma_map dma_map = {
.argsz = sizeof(dma_map),
.flags = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE,
};

if (argc != 2) {
usage(argv[0]);
return -1;
}

ret = sscanf(argv[1], "%04x:%02x:%02x.%d", &seg, &bus, &slot, &func);
if (ret != 4) {
fprintf(stderr, "Invalid device\n");
usage(argv[0]);
return -1;
}

/* Boilerplate vfio setup */
container = open("/dev/vfio/vfio", O_RDWR);
if (container < 0) {
fprintf(stderr, "Failed to open /dev/vfio/vfio, %d (%s)\n",
container, strerror(errno));
return container;
}

snprintf(path, sizeof(path),
"/sys/bus/pci/devices/%04x:%02x:%02x.%01x/",
seg, bus, slot, func);

ret = stat(path, &st);
if (ret < 0) {
fprintf(stderr, "No such device\n");
return ret;
}

strncat(path, "iommu_group", sizeof(path) - strlen(path) - 1);

len = readlink(path, iommu_group_path, sizeof(iommu_group_path));
if (len <= 0) {
fprintf(stderr, "No iommu_group for device\n");
return -1;
}

iommu_group_path[len] = 0;
group_name = basename(iommu_group_path);

if (sscanf(group_name, "%d", &groupid) != 1) {
fprintf(stderr, "Unknown group\n");
return -1;
}

snprintf(path, sizeof(path), "/dev/vfio/%d", groupid);
group = open(path, O_RDWR);
if (group < 0) {
fprintf(stderr, "Failed to open %s, %d (%s)\n",
path, group, strerror(errno));
return group;
}

ret = ioctl(group, VFIO_GROUP_GET_STATUS, &group_status);
if (ret) {
fprintf(stderr, "ioctl(VFIO_GROUP_GET_STATUS) failed\n");
return ret;
}

if (!(group_status.flags & VFIO_GROUP_FLAGS_VIABLE)) {
fprintf(stderr,
"Group not viable, all devices attached to vfio?\n");
return -1;
}

ret = ioctl(group, VFIO_GROUP_SET_CONTAINER, &container);
if (ret) {
fprintf(stderr, "Failed to set group container\n");
return ret;
}

ret = ioctl(container, VFIO_SET_IOMMU, VFIO_TYPE1_IOMMU);
if (ret) {
fprintf(stderr, "Failed to set IOMMU\n");
return ret;
}

snprintf(path, sizeof(path), "%04x:%02x:%02x.%d", seg, bus, slot, func);

device = ioctl(group, VFIO_GROUP_GET_DEVICE_FD, path);
if (device < 0) {
fprintf(stderr, "Failed to get device\n");
return -ENODEV;
}

config_info.index = VFIO_PCI_CONFIG_REGION_INDEX;
ret = ioctl(device, VFIO_DEVICE_GET_REGION_INFO, &config_info);
if (ret) {
fprintf(stderr, "Failed to get config space region info\n");
return ret;
}

for (i = 0; i < 6; i++) {
if (pread(device, &bar, sizeof(bar),
config_info.offset + PCI_BASE_ADDRESS_0 + (4 * i)) !=
sizeof(bar)) {
fprintf(stderr, "Error reading BAR%d\n", i);
return -errno;
}

if (!(bar & PCI_BASE_ADDRESS_SPACE)) {
break;

tryagain:
if (bar & PCI_BASE_ADDRESS_MEM_TYPE_64)
i++;
}
}

if (i >= 6) {
fprintf(stderr, "No memory BARs found\n");
return -ENODEV;
}

region_info.index = VFIO_PCI_BAR0_REGION_INDEX + i;
ret = ioctl(device, VFIO_DEVICE_GET_REGION_INFO, &region_info);
if (ret) {
fprintf(stderr, "Failed to get BAR%d region info\n", i);
return ret;
}

if (!(region_info.flags & VFIO_REGION_INFO_FLAG_MMAP)) {
printf("No mmap support, try next\n");
goto tryagain;
}

if (region_info.size < getpagesize()) {
printf("Too small for mmap, try next\n");
goto tryagain;
}

map = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE,
MAP_SHARED, device, region_info.offset);
if (map == MAP_FAILED) {
fprintf(stderr, "Error mmap'ing BAR: %m\n");
goto tryagain;
}

dma_map.size = getpagesize();
dma_map.vaddr = (__u64)map;
dma_map.iova = 1024 * 1024 * 1024; /* 1GB IOVA, arbitrary */

ret = ioctl(container, VFIO_IOMMU_MAP_DMA, &dma_map);
if (ret) {
fprintf(stderr, "Failed to DMA map: %m\n");
return ret;
}

printf("Passed\n");
return 0;
}