[Xen-changelog] [xen stable-4.9] x86/AMD: flush TLB after ucode update

[patchbot@xxxxxxx]

commit 9f1b0e609e7aef955c5a0f2dab1fcb961100d195
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Feb 1 12:06:49 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Feb 1 12:06:49 2019 +0100

    x86/AMD: flush TLB after ucode update
    
    The increased number of messages (spec_ctrl.c:print_details()) within a
    certain time window made me notice some slowness of boot time screen
    output. Experimentally I've narrowed the time window to be from
    immediately after the early ucode update on the BSP to the PAT write in
    cpu_init(), which upon further investigation has an effect because of
    the full TLB flush that's implied by that write.
    
    For that reason, as a workaround, flush the TLB of the mapping of the
    page that holds the blob. Note that flushing just a single page is
    sufficient: As per verify_patch_size() patch size can't exceed 4k, and
    the way xmalloc() works the blob can't be crossing a page boundary.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Brian Woods <brian.woods@xxxxxxx>
    master commit: f19a199281a23725beb73bef61eb8964d8e225ce
    master date: 2019-01-28 17:40:39 +0100
---
 xen/arch/x86/microcode_amd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
index 53f9f548cd..835d0f9906 100644
--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -218,6 +218,12 @@ static int apply_microcode(unsigned int cpu)
 
     spin_unlock_irqrestore(&microcode_update_lock, flags);
 
+    /*
+     * Some processors leave the ucode blob mapping as UC after the update.
+     * Flush the mapping to regain normal cacheability.
+     */
+    flush_area_local(hdr, FLUSH_TLB_GLOBAL | FLUSH_ORDER(0));
+
     /* check current patch id and patch's id for match */
     if ( hw_err || (rev != hdr->patch_id) )
     {
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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