Patchwork pseries: Don't try to munmap() a malloc()ed TCE table

For the pseries machine, TCE (IOMMU) tables can either be directly
malloc()ed in qemu or, when running on a KVM which supports it, mmap()ed
from a KVM ioctl.  The latter option is used when available, because it
allows the (frequent bottlenext) H_PUT_TCE hypercall to be KVM accelerated.
However, even when KVM is persent, TCE acceleration is not always possible.
Only KVM HV supports this ioctl(), not KVM PR, or the kernel could run out
of contiguous memory to allocate the new table.  In this case we need to
fall back on the malloc()ed table.

When a device is removed, and we need to remove the TCE table, we need to
either munmap() or free() the table as appropriate for how it was
allocated.  The code is supposed to do that, but we buggily fail to
initialize the tcet->fd variable in the malloc() case, which is used as a
flag to determine which is the right choice.

This patch fixes the bug, and cleans up error messages relating to this
path while we're at it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 target-ppc/kvm.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

Am 08.02.2012 06:53, schrieb David Gibson:
> For the pseries machine, TCE (IOMMU) tables can either be directly
> malloc()ed in qemu or, when running on a KVM which supports it, mmap()ed
> from a KVM ioctl.  The latter option is used when available, because it
> allows the (frequent bottlenext) H_PUT_TCE hypercall to be KVM accelerated.
> However, even when KVM is persent, TCE acceleration is not always possible.
> Only KVM HV supports this ioctl(), not KVM PR, or the kernel could run out
> of contiguous memory to allocate the new table.  In this case we need to
> fall back on the malloc()ed table.
> 
> When a device is removed, and we need to remove the TCE table, we need to
> either munmap() or free() the table as appropriate for how it was
> allocated.  The code is supposed to do that, but we buggily fail to
> initialize the tcet->fd variable in the malloc() case, which is used as a
> flag to determine which is the right choice.
> 
> This patch fixes the bug, and cleans up error messages relating to this
> path while we're at it.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Looks okay except that your fprintf()s should use PRIx32 for uint32_t
liobn for safety (no difference on Linux).

Andreas

> ---
>  target-ppc/kvm.c |   12 ++++++++++--
>  1 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
> index 50cfa02..90c6941 100644
> --- a/target-ppc/kvm.c
> +++ b/target-ppc/kvm.c
> @@ -843,12 +843,18 @@ void *kvmppc_create_spapr_tce(uint32_t liobn, uint32_t window_size, int *pfd)
>      int fd;
>      void *table;
>  
> +    /* Must set fd to -1 so we don't try to munmap when called for
> +     * destroying the table, which the upper layers -will- do
> +     */
> +    *pfd = -1;
>      if (!cap_spapr_tce) {
>          return NULL;
>      }
>  
>      fd = kvm_vm_ioctl(kvm_state, KVM_CREATE_SPAPR_TCE, &args);
>      if (fd < 0) {
> +        fprintf(stderr, "KVM: Failed to create TCE table for liobn 0x%x\n",
> +                liobn);
>          return NULL;
>      }
>  
> @@ -857,6 +863,8 @@ void *kvmppc_create_spapr_tce(uint32_t liobn, uint32_t window_size, int *pfd)
>  
>      table = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
>      if (table == MAP_FAILED) {
> +        fprintf(stderr, "KVM: Failed to map TCE table for liobn 0x%x\n",
> +                liobn);
>          close(fd);
>          return NULL;
>      }
> @@ -876,8 +884,8 @@ int kvmppc_remove_spapr_tce(void *table, int fd, uint32_t window_size)
>      len = (window_size / SPAPR_VIO_TCE_PAGE_SIZE)*sizeof(VIOsPAPR_RTCE);
>      if ((munmap(table, len) < 0) ||
>          (close(fd) < 0)) {
> -        fprintf(stderr, "KVM: Unexpected error removing KVM SPAPR TCE "
> -                "table: %s", strerror(errno));
> +        fprintf(stderr, "KVM: Unexpected error removing TCE table: %s",
> +                strerror(errno));
>          /* Leak the table */
>      }
>