From 3125ca0da2d80123823ff24148467504aa4c7f13 Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Thu, 15 May 2025 14:38:51 +0200 Subject: [PATCH] x86/hvm: limit memory type cache flush to running domains MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Avoid the cache flush if the domain is not yet running. There shouldn't be any cached data resulting from domain accesses that need flushing, as the domain hasn't run yet. There can be data in the caches as a result of Xen and/or toolstack behavior. Ideally we would do a cache flush strictly before starting the domain, however doing so only makes sense once we can guarantee there are no leftover mappings of the affected ranges with cacheable attributes, otherwise the CPU can speculatively populate the cache with data from those ranges. No change in domain observable behavior intended. Signed-off-by: Roger Pau Monné Reviewed-by: Jan Beulich --- xen/arch/x86/hvm/mtrr.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/hvm/mtrr.c b/xen/arch/x86/hvm/mtrr.c index 402a1d9263..8e1e15af8d 100644 --- a/xen/arch/x86/hvm/mtrr.c +++ b/xen/arch/x86/hvm/mtrr.c @@ -783,7 +783,13 @@ HVM_REGISTER_SAVE_RESTORE(MTRR, hvm_save_mtrr_msr, NULL, hvm_load_mtrr_msr, 1, void memory_type_changed(struct domain *d) { if ( (is_iommu_enabled(d) || cache_flush_permitted(d)) && - d->vcpu && d->vcpu[0] && p2m_memory_type_changed(d) ) + d->vcpu && d->vcpu[0] && p2m_memory_type_changed(d) && + /* + * Do the p2m type-change, but skip the cache flush if the domain is + * not yet running. The check for creation_finished must strictly be + * done after the call to p2m_memory_type_changed(). + */ + d->creation_finished ) { flush_all(FLUSH_CACHE); }