linux-kernel - Re: [GIT PULL] x86/mm changes for v4.21

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Date:   Thu, 7 Feb 2019 11:18:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [GIT PULL] x86/mm changes for v4.21

On Wed, Feb 06, 2019 at 04:17:42PM -0800, Luck, Tony wrote:

> fe0937b24ff5 ("x86/mm/cpa: Fold cpa_flush_range() and cpa_flush_array() into a single cpa_flush() function")

Boris pointed me at this gem:

  c7486104a5ce ("x86/mce: Fix set_mce_nospec() to avoid #GP fault")

(can I just revel at the pure awesome grossness of that)

But we then see my above commit having:

@@ -1732,11 +1685,6 @@ static int change_page_attr_set_clr(unsigned long *addr, int numpages,
			 */
			WARN_ON_ONCE(1);
		}
-               /*
-                * Save address for cache flush. *addr is modified in the call
-                * to __change_page_attr_set_clr() below.
-                */
-               baddr = make_addr_canonical_again(*addr);

Where I clearly got distracted by that excellent comment..


So now the question is where to put it back in, I'm thinking this might
want to be in __cpa_addr().

Something like so?

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 4f8972311a77..319b767484fb 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -230,6 +230,28 @@ static bool __cpa_pfn_in_highmap(unsigned long pfn)
 
 #endif
 
+/*
+ * Machine check recovery code needs to change cache mode of poisoned
+ * pages to UC to avoid speculative access logging another error. But
+ * passing the address of the 1:1 mapping to set_memory_uc() is a fine
+ * way to encourage a speculative access. So we cheat and flip the top
+ * bit of the address. This works fine for the code that updates the
+ * page tables. But at the end of the process we need to flush the cache
+ * and the non-canonical address causes a #GP fault when used by the
+ * CLFLUSH instruction.
+ *
+ * But in the common case we already have a canonical address. This code
+ * will fix the top bit if needed and is a no-op otherwise.
+ */
+static inline unsigned long make_addr_canonical_again(unsigned long addr)
+{
+#ifdef CONFIG_X86_64
+	return (long)(addr << 1) >> 1;
+#else
+	return addr;
+#endif
+}
+
 static unsigned long __cpa_addr(struct cpa_data *cpa, unsigned long idx)
 {
 	if (cpa->flags & CPA_PAGES_ARRAY) {
@@ -244,7 +266,7 @@ static unsigned long __cpa_addr(struct cpa_data *cpa, unsigned long idx)
 	if (cpa->flags & CPA_ARRAY)
 		return cpa->vaddr[idx];
 
-	return *cpa->vaddr + idx * PAGE_SIZE;
+	return make_addr_canonical_again(*cpa->vaddr + idx * PAGE_SIZE);
 }
 
 /*
@@ -1627,29 +1649,6 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
 	return ret;
 }
 
-/*
- * Machine check recovery code needs to change cache mode of poisoned
- * pages to UC to avoid speculative access logging another error. But
- * passing the address of the 1:1 mapping to set_memory_uc() is a fine
- * way to encourage a speculative access. So we cheat and flip the top
- * bit of the address. This works fine for the code that updates the
- * page tables. But at the end of the process we need to flush the cache
- * and the non-canonical address causes a #GP fault when used by the
- * CLFLUSH instruction.
- *
- * But in the common case we already have a canonical address. This code
- * will fix the top bit if needed and is a no-op otherwise.
- */
-static inline unsigned long make_addr_canonical_again(unsigned long addr)
-{
-#ifdef CONFIG_X86_64
-	return (long)(addr << 1) >> 1;
-#else
-	return addr;
-#endif
-}
-
-
 static int change_page_attr_set_clr(unsigned long *addr, int numpages,
 				    pgprot_t mask_set, pgprot_t mask_clr,
 				    int force_split, int in_flag,