[PATCH 1/9] x86/mm/pat: flush the TLB when only an alias mapping changed

["Mike Rapoport (Microsoft)" <rppt@kernel.org>]

CPA flushes the TLB only when CPA_FLUSHTLB is set. cpa_process_alias()
sets the flag only in alias_cpa and never in the original request.

When the requested range already has the new protection and only its
alias changes, the alias keeps stale TLB entries. For example:

	/* the vmalloc mapping is created read-only */
	p = vmap(pages, nr, VM_MAP, PAGE_KERNEL_RO);

	/* only the direct map changes and nothing is flushed */
	set_memory_ro((unsigned long)p, nr);

Setting ->force_flush_all in cpa_process_alias() does not help: it only
chooses how the TLB is flushed, and cpa_flush() is skipped entirely
without CPA_FLUSHTLB.

Worse, when the alias wasn't changed at all, for example when the primary
mapping changes from ROX to RO or vice versa, ->force_flush_all in
cpa_process_alias() causes an unnecessary flush of all TLBs.

Propagate CPA_FLUSHTLB from the alias update to the original request, and
flush the entire TLB only when an alias actually changed.

Fixes: ab5130186d74 ("x86/mm/cpa: Flush direct map alias during cpa")
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 arch/x86/mm/pat/set_memory.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index b1d5c5a0ffb41..fb2413cb8d314 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1975,7 +1975,8 @@ static int cpa_process_alias(struct cpa_data *cpa)
 
 		alias_cpa = *cpa;
 		alias_cpa.vaddr = &laddr;
-		alias_cpa.flags &= ~(CPA_PAGES_ARRAY | CPA_ARRAY);
+		alias_cpa.flags &= ~(CPA_PAGES_ARRAY | CPA_ARRAY |
+				     CPA_FLUSHTLB);
 		alias_cpa.curpage = 0;
 
 		/* Directmap always has NX set, do not modify. */
@@ -1984,9 +1985,11 @@ static int cpa_process_alias(struct cpa_data *cpa)
 			alias_cpa.mask_set.pgprot &= ~_PAGE_NX;
 		}
 
-		cpa->force_flush_all = 1;
-
 		ret = __change_page_attr_set_clr(&alias_cpa, 0);
+		if (alias_cpa.flags & CPA_FLUSHTLB) {
+			cpa->flags |= CPA_FLUSHTLB;
+			cpa->force_flush_all = 1;
+		}
 		if (ret)
 			return ret;
 	}
@@ -2003,7 +2006,8 @@ static int cpa_process_alias(struct cpa_data *cpa)
 					       __START_KERNEL_map - phys_base;
 		alias_cpa = *cpa;
 		alias_cpa.vaddr = &temp_cpa_vaddr;
-		alias_cpa.flags &= ~(CPA_PAGES_ARRAY | CPA_ARRAY);
+		alias_cpa.flags &= ~(CPA_PAGES_ARRAY | CPA_ARRAY |
+				     CPA_FLUSHTLB);
 		alias_cpa.curpage = 0;
 
 		/*
@@ -2015,12 +2019,15 @@ static int cpa_process_alias(struct cpa_data *cpa)
 			alias_cpa.mask_set.pgprot &= ~_PAGE_NX;
 		}
 
-		cpa->force_flush_all = 1;
 		/*
 		 * The high mapping range is imprecise, so ignore the
 		 * return value.
 		 */
 		__change_page_attr_set_clr(&alias_cpa, 0);
+		if (alias_cpa.flags & CPA_FLUSHTLB) {
+			cpa->flags |= CPA_FLUSHTLB;
+			cpa->force_flush_all = 1;
+		}
 	}
 #endif
 

-- 
2.53.0