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Re: [PATCH] virtiofs: Relax DAX window protection for ppc
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH] virtiofs: Relax DAX window protection for ppc |
Date: |
Tue, 3 Dec 2019 10:07:08 +0000 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
* Fabiano Rosas (address@hidden) wrote:
> When setting up the DAX window during the virtiofs driver probe inside
> the guest, the Linux arch-specific function arch_add_memory is called,
> which on ppc tries to do a cache flush [1] of the recently added
> memory. At this point the window is mmap'ed PROT_NONE by QEMU, which
> causes the following:
>
> <snip>
> [ 10.136703] virtio_fs virtio0: Cache len: 0x80000000 @ 0x210000000000
> [ 10.165106] radix-mmu: Mapped 0xc000210000000000-0xc000210080000000 with
> 1.00 GiB pages
> error: kvm run failed Bad address
> NIP c000000000072350 LR c000000000072304 CTR 0000000001000000 XER
> 0000000020040000 CPU#0
> MSR 8000000002009033 HID0 0000000000000000 HF 8000000000000000 iidx 3 didx 3
> TB 00000000 00000000 DECR 0
> GPR00 c000000000072304 c0000000fa383100 c000000001190300 0000000000000000
> GPR04 0000000000000001 0000000000000000 c0000000fa383208 0000000000000080
> GPR08 c000210000000000 000000008000007f 0000000001000000 6874697720303030
> <snip>
>
> The problem is the same for the memory device removal path
> (e.g. during filesystem unmount).
>
> Since powerpc expects the memory to be accessible during device
> addition/removal, this patch makes the DAX window readable at creation
> and after virtio-fs unmap.
>
> 1 -
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fb5924fd
>
> Signed-off-by: Fabiano Rosas <address@hidden>
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
Thanks, I'll do a pull after the tree opens again.
Dave
> ---
> hw/virtio/vhost-user-fs.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c
> index 455e97beea..92958797d0 100644
> --- a/hw/virtio/vhost-user-fs.c
> +++ b/hw/virtio/vhost-user-fs.c
> @@ -24,6 +24,16 @@
> #include "exec/address-spaces.h"
> #include "trace.h"
>
> +/*
> + * The powerpc kernel code expects the memory to be accessible during
> + * addition/removal.
> + */
> +#if defined(TARGET_PPC64) && defined(CONFIG_LINUX)
> +#define DAX_WINDOW_PROT PROT_READ
> +#else
> +#define DAX_WINDOW_PROT PROT_NONE
> +#endif
> +
> uint64_t vhost_user_fs_slave_map(struct vhost_dev *dev, VhostUserFSSlaveMsg
> *sm,
> int fd)
> {
> @@ -133,8 +143,8 @@ uint64_t vhost_user_fs_slave_unmap(struct vhost_dev *dev,
> VhostUserFSSlaveMsg *s
> continue;
> }
>
> - ptr = mmap(cache_host + sm->c_offset[i], sm->len[i],
> - PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
> + ptr = mmap(cache_host + sm->c_offset[i], sm->len[i], DAX_WINDOW_PROT,
> + MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
> if (ptr != (cache_host + sm->c_offset[i])) {
> res = -errno;
> fprintf(stderr, "%s: mmap failed (%s) [%d] %"
> @@ -485,8 +495,9 @@ static void vuf_device_realize(DeviceState *dev, Error
> **errp)
>
> if (fs->conf.cache_size) {
> /* Anonymous, private memory is not counted as overcommit */
> - cache_ptr = mmap(NULL, fs->conf.cache_size, PROT_NONE,
> + cache_ptr = mmap(NULL, fs->conf.cache_size, DAX_WINDOW_PROT,
> MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +
> if (cache_ptr == MAP_FAILED) {
> error_setg(errp, "Unable to mmap blank cache");
> return;
> --
> 2.23.0
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK