Re: [PATCH] x86/mm/cpa: Flush direct map alias during cpa

[Peter Zijlstra]

On Wed, Apr 22, 2020 at 08:13:55PM -0700, Rick Edgecombe wrote:
> Change cpa_flush() to always flush_tlb_all(), as it previously did. As an
> optimization, cpa_flush() was changed to optionally only flush the range
> in "struct cpa_data *data" if it was small enough. However, this range
> does not include any direct map aliases changed in cpa_process_alias().
> So small set_memory_() calls that touch that alias don't get the direct
> map changes flushed. This situation can happen when the virtual address
> taking variants are passed an address in vmalloc or modules space.

Wouldn't something like so make more sense?

---
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 59eca6a94ce7..b8c55a2e402d 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -43,7 +43,8 @@ struct cpa_data {
 	unsigned long	pfn;
 	unsigned int	flags;
 	unsigned int	force_split		: 1,
-			force_static_prot	: 1;
+			force_static_prot	: 1,
+			force_flush_all		: 1;
 	struct page	**pages;
 };
 
@@ -355,10 +356,10 @@ static void cpa_flush(struct cpa_data *data, int cache)
 		return;
 	}
 
-	if (cpa->numpages <= tlb_single_page_flush_ceiling)
-		on_each_cpu(__cpa_flush_tlb, cpa, 1);
-	else
+	if (cpa->force_flush_all || cpa->numpages > tlb_single_page_flush_ceiling)
 		flush_tlb_all();
+	else
+		on_each_cpu(__cpa_flush_tlb, cpa, 1);
 
 	if (!cache)
 		return;
@@ -1598,6 +1599,8 @@ static int cpa_process_alias(struct cpa_data *cpa)
 		alias_cpa.flags &= ~(CPA_PAGES_ARRAY | CPA_ARRAY);
 		alias_cpa.curpage = 0;
 
+		cpa->force_flush_all = 1;
+
 		ret = __change_page_attr_set_clr(&alias_cpa, 0);
 		if (ret)
 			return ret;
@@ -1618,6 +1621,7 @@ static int cpa_process_alias(struct cpa_data *cpa)
 		alias_cpa.flags &= ~(CPA_PAGES_ARRAY | CPA_ARRAY);
 		alias_cpa.curpage = 0;
 
+		cpa->force_flush_all = 1;
 		/*
 		 * The high mapping range is imprecise, so ignore the
 		 * return value.