Re: [PATCH] virtiofs: Relax DAX window protection for ppc

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Fabiano Rosas <farosas@linux.ibm.com>
Cc: virtio-fs@redhat.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org,
	stefanha@redhat.com
Subject: Re: [PATCH] virtiofs: Relax DAX window protection for ppc
Date: Tue, 3 Dec 2019 10:07:08 +0000	[thread overview]
Message-ID: <20191203100708.GA3078@work-vm> (raw)
In-Reply-To: <20191202202639.102322-1-farosas@linux.ibm.com>

* Fabiano Rosas (farosas@linux.ibm.com) 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 <farosas@linux.ibm.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

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 / dgilbert@redhat.com / Manchester, UK