Hello,
> On 26 Sep 2020, at 9:55 pm, Julien Grall <jul...@xen.org> wrote:
>
> From: Julien Grall <jgr...@amazon.com>
>
> Commit 022387ee1ad3 "xen/arm: mm: Don't open-code Xen PT update in
> {set, clear}_fixmap()" enforced that each set_fixmap() should be
> paired with a clear_fixmap(). Any failure to follow the model would
> result to a platform crash.
>
> Unfortunately, the use of fixmap in the ACPI code was overlooked as it
> is calling set_fixmap() but not clear_fixmap().
>
> The function __acpi_os_map_table() is reworked so:
> - We know before the mapping whether the fixmap region is big
> enough for the mapping.
> - It will fail if the fixmap is always inuse.
>
> The function __acpi_os_unmap_table() will now call clear_fixmap().
>
> Reported-by: Wei Xu <xuw...@hisilicon.com>
> Signed-off-by: Julien Grall <jgr...@amazon.com>
Reviewed-by: Rahul Singh <rahul.si...@arm.com>
Tested-by: Rahul Singh <rahul.si...@arm.com>
>
> ---
>
> The discussion on the original thread [1] suggested to also zap it on
> x86. This is technically not necessary today, so it is left alone for
> now.
>
> I looked at making the fixmap code common but the index are inverted
> between Arm and x86.
>
> [1] https://lore.kernel.org/xen-devel/5e26c935.9080...@hisilicon.com/
> ---
> xen/arch/arm/acpi/lib.c | 75 +++++++++++++++++++++++++++++++----------
> 1 file changed, 58 insertions(+), 17 deletions(-)
>
> diff --git a/xen/arch/arm/acpi/lib.c b/xen/arch/arm/acpi/lib.c
> index 2192a5519171..eebaca695562 100644
> --- a/xen/arch/arm/acpi/lib.c
> +++ b/xen/arch/arm/acpi/lib.c
> @@ -25,38 +25,79 @@
> #include <xen/init.h>
> #include <xen/mm.h>
>
> +static bool fixmap_inuse;
> +
> char *__acpi_map_table(paddr_t phys, unsigned long size)
> {
> - unsigned long base, offset, mapped_size;
> - int idx;
> + unsigned long base, offset;
> + mfn_t mfn;
> + unsigned int idx;
>
> /* No arch specific implementation after early boot */
> if ( system_state >= SYS_STATE_boot )
> return NULL;
>
> offset = phys & (PAGE_SIZE - 1);
> - mapped_size = PAGE_SIZE - offset;
> - set_fixmap(FIXMAP_ACPI_BEGIN, maddr_to_mfn(phys), PAGE_HYPERVISOR);
> - base = FIXMAP_ADDR(FIXMAP_ACPI_BEGIN);
> + base = FIXMAP_ADDR(FIXMAP_ACPI_BEGIN) + offset;
> +
> + /* Check the fixmap is big enough to map the region */
> + if ( (FIXMAP_ADDR(FIXMAP_ACPI_END) + PAGE_SIZE - base) < size )
> + return NULL;
> +
> + /* With the fixmap, we can only map one region at the time */
> + if ( fixmap_inuse )
> + return NULL;
>
> - /* Most cases can be covered by the below. */
> + fixmap_inuse = true;
> +
> + size += offset;
> + mfn = maddr_to_mfn(phys);
> idx = FIXMAP_ACPI_BEGIN;
> - while ( mapped_size < size )
> - {
> - if ( ++idx > FIXMAP_ACPI_END )
> - return NULL; /* cannot handle this */
> - phys += PAGE_SIZE;
> - set_fixmap(idx, maddr_to_mfn(phys), PAGE_HYPERVISOR);
> - mapped_size += PAGE_SIZE;
> - }
>
> - return ((char *) base + offset);
> + do {
> + set_fixmap(idx, mfn, PAGE_HYPERVISOR);
> + size -= min(size, (unsigned long)PAGE_SIZE);
> + mfn = mfn_add(mfn, 1);
> + idx++;
> + } while ( size > 0 );
> +
> + return (char *)base;
> }
>
> bool __acpi_unmap_table(void *ptr, unsigned long size)
> {
> - return ( vaddr >= FIXMAP_ADDR(FIXMAP_ACPI_BEGIN) &&
> - vaddr < (FIXMAP_ADDR(FIXMAP_ACPI_END) + PAGE_SIZE) );
> + vaddr_t vaddr = (vaddr_t)ptr;
> + unsigned int idx;
> +
> + /* We are only handling fixmap address in the arch code */
> + if ( vaddr < FIXMAP_ADDR(FIXMAP_ACPI_BEGIN) ||
> + vaddr >= FIXMAP_ADDR(FIXMAP_ACPI_END) )
> + return false;
> +
> + /*
> + * __acpi_map_table() will always return a pointer in the first page
> + * for the ACPI fixmap region. The caller is expected to free with
> + * the same address.
> + */
> + ASSERT((vaddr & PAGE_MASK) == FIXMAP_ADDR(FIXMAP_ACPI_BEGIN));
> +
> + /* The region allocated fit in the ACPI fixmap region. */
> + ASSERT(size < (FIXMAP_ADDR(FIXMAP_ACPI_END) + PAGE_SIZE - vaddr));
> + ASSERT(fixmap_inuse);
> +
> + fixmap_inuse = false;
> +
> + size += FIXMAP_ADDR(FIXMAP_ACPI_BEGIN) - vaddr;
> + idx = FIXMAP_ACPI_BEGIN;
> +
> + do
> + {
> + clear_fixmap(idx);
> + size -= min(size, (unsigned long)PAGE_SIZE);
> + idx++;
> + } while ( size > 0 );
> +
> + return true;
> }
>
> /* True to indicate PSCI 0.2+ is implemented */
> --
> 2.17.1
>
>
Regards,
Rahul
