lkml.org 
[lkml]   [2013]   [Sep]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 3/5] xen/smp: Update pv_lock_ops functions before alternative code starts under PVHVM
    Date
    Before this patch we would patch all of the pv_lock_ops sites
    using alternative assembler. Then later in the bootup cycle
    change the unlock_kick and lock_spinning to the Xen specific -
    without re patching.

    That meant that for the core of the kernel we would be running
    with the baremetal version of unlock_kick and lock_spinning while
    for modules we would have the proper Xen specific slowpaths.

    As most of the module uses some API from the core kernel that ended
    up with slowpath lockers waiting forever to be kicked (b/c they
    would be using the Xen specific slowpath logic). And the
    kick never came b/c the unlock path that was taken was the
    baremetal one.

    On PV we do not have the problem as we initialise before the
    alternative code kicks in.

    The fix is to make the updating of the pv_lock_ops function
    be done before the alternative code starts patching.

    Note that this patch fixes issues discovered by commit
    f10cd522c5fbfec9ae3cc01967868c9c2401ed23.
    ("xen: disable PV spinlocks on HVM") wherein it mentioned

    PV spinlocks cannot possibly work with the current code because they are
    enabled after pvops patching has already been done, and because PV
    spinlocks use a different data structure than native spinlocks so we
    cannot switch between them dynamically.

    The first problem is solved by this patch.

    The second problem has been solved by commit
    816434ec4a674fcdb3c2221a6dffdc8f34020550
    (Merge branch 'x86-spinlocks-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip)

    P.S.
    There is still the commit 70dd4998cb85f0ecd6ac892cc7232abefa432efb
    (xen/spinlock: Disable IRQ spinlock (PV) allocation on PVHVM) to
    revert but that can be done later after all other bugs have been
    fixed.

    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Reviewed-by: David Vrabel <david.vrabel@citrix.com>
    ---
    arch/x86/xen/smp.c | 19 ++++++++++++++-----
    1 file changed, 14 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
    index c21b825..d1e4777 100644
    --- a/arch/x86/xen/smp.c
    +++ b/arch/x86/xen/smp.c
    @@ -273,12 +273,20 @@ static void __init xen_smp_prepare_boot_cpu(void)
    BUG_ON(smp_processor_id() != 0);
    native_smp_prepare_boot_cpu();

    - /* We've switched to the "real" per-cpu gdt, so make sure the
    - old memory can be recycled */
    - make_lowmem_page_readwrite(xen_initial_gdt);
    + if (xen_pv_domain()) {
    + /* We've switched to the "real" per-cpu gdt, so make sure the
    + old memory can be recycled */
    + make_lowmem_page_readwrite(xen_initial_gdt);

    - xen_filter_cpu_maps();
    - xen_setup_vcpu_info_placement();
    + xen_filter_cpu_maps();
    + xen_setup_vcpu_info_placement();
    + }
    + /*
    + * The alternative logic (which patches the unlock/lock) runs before
    + * the smp bootup up code is activated. Hence we need to set this up
    + * the core kernel is being patched. Otherwise we will have only
    + * modules patched but not core code.
    + */
    xen_init_spinlocks();
    }

    @@ -737,4 +745,5 @@ void __init xen_hvm_smp_init(void)
    smp_ops.cpu_die = xen_hvm_cpu_die;
    smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
    smp_ops.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi;
    + smp_ops.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu;
    }
    --
    1.8.3.1


    \
     
     \ /
      Last update: 2013-09-09 18:21    [W:7.108 / U:0.028 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site