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[PATCH] x86/MTRR: constrain AP sync and BSP restore
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 27 Mar 2025 10:54:23 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 27 Mar 2025 09:54:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
mtrr_set_all() has quite a bit of overhead, which is entirely useless
when set_mtrr_state() really does nothing. Furthermore, with
mtrr_state.def_type never initialized from hardware, post_set()'s
unconditional writing of the MSR means would leave us running in UC
mode after the sync.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
--- a/xen/arch/x86/cpu/mtrr/main.c
+++ b/xen/arch/x86/cpu/mtrr/main.c
@@ -605,13 +605,15 @@ void mtrr_aps_sync_begin(void)
void mtrr_aps_sync_end(void)
{
- set_mtrr(~0U, 0, 0, 0);
+ if (mtrr_if)
+ set_mtrr(~0U, 0, 0, 0);
hold_mtrr_updates_on_aps = 0;
}
void mtrr_bp_restore(void)
{
- mtrr_set_all();
+ if (mtrr_if)
+ mtrr_set_all();
}
static int __init cf_check mtrr_init_finialize(void)
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