From 2fd3628fa6c4c22c4a1c2f4587f9e5ddf43bb698 Mon Sep 17 00:00:00 2001 From: Teddy Astie Date: Thu, 31 Jul 2025 09:51:13 +0200 Subject: [PATCH] x86/svm: Always flush TLB using TLB_CTRL_FLUSH_ALL Xen currently uses an ASID scheme where: - ASIDs are cycled where a "TLB flush" is performed - When ASIDs wrap around, perform a full TLB flush - In exceptional cases, stop using ASIDs However, the TLB control mode used only flushes the current active ASID of the logical processor. Which mean that will supply "stale" ASIDs (not flushed), because it hasn't been actually flushed (TLB_CTRL_FLUSH_ASID only performs a TLB flush of the ASID set in VMCB). This affects CPUs where flush-by-asid is available (Fam15h (2011) and later). To fix this, always flush all ASIDs even when flush-by-asid is available. Fixes: 64b1da5a2fcf ("x86/svm: Use flush-by-asid when available") Signed-off-by: Teddy Astie Reviewed-by: Jan Beulich Reviewed-by: Andrew Cooper master commit: 68871b1f9b8034fef12826610b0f590fd7c212ed master date: 2025-07-23 15:23:44 +0200 --- xen/arch/x86/hvm/svm/asid.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/hvm/svm/asid.c b/xen/arch/x86/hvm/svm/asid.c index 7977a8e86b..b2ca639539 100644 --- a/xen/arch/x86/hvm/svm/asid.c +++ b/xen/arch/x86/hvm/svm/asid.c @@ -46,9 +46,8 @@ void svm_asid_handle_vmrun(void) if ( vmcb_get_asid(vmcb) != p_asid->asid ) vmcb_set_asid(vmcb, p_asid->asid); - vmcb->tlb_control = - !need_flush ? TLB_CTRL_NO_FLUSH : - cpu_has_svm_flushbyasid ? TLB_CTRL_FLUSH_ASID : TLB_CTRL_FLUSH_ALL; + /* We can't rely on TLB_CTRL_FLUSH_ASID as all ASIDs are stale here. */ + vmcb->tlb_control = need_flush ? TLB_CTRL_FLUSH_ALL : TLB_CTRL_NO_FLUSH; } /*