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    Subject[PATCH 4.9 120/206] iommu/amd: Fix the left value check of cmd buffer
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Huang Rui <ray.huang@amd.com>

    commit 432abf68a79332282329286d190e21fe3ac02a31 upstream.

    The generic command buffer entry is 128 bits (16 bytes), so the offset
    of tail and head pointer should be 16 bytes aligned and increased with
    0x10 per command.

    When cmd buf is full, head = (tail + 0x10) % CMD_BUFFER_SIZE.

    So when left space of cmd buf should be able to store only two
    command, we should be issued one COMPLETE_WAIT additionally to wait
    all older commands completed. Then the left space should be increased
    after IOMMU fetching from cmd buf.

    So left check value should be left <= 0x20 (two commands).

    Signed-off-by: Huang Rui <ray.huang@amd.com>
    Fixes: ac0ea6e92b222 ('x86/amd-iommu: Improve handling of full command buffer')
    Signed-off-by: Joerg Roedel <jroedel@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/iommu/amd_iommu.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/iommu/amd_iommu.c
    +++ b/drivers/iommu/amd_iommu.c
    @@ -1021,7 +1021,7 @@ again:
    next_tail = (tail + sizeof(*cmd)) % CMD_BUFFER_SIZE;
    left = (head - next_tail) % CMD_BUFFER_SIZE;

    - if (left <= 2) {
    + if (left <= 0x20) {
    struct iommu_cmd sync_cmd;
    int ret;


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