linux-kernel - Re: [PATCH 0/4] x86/mm/cpa: Fix cpa-array TLB invalidation

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Date:   Mon, 3 Dec 2018 16:41:02 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "StDenis, Tom" <Tom.StDenis@....com>
Cc:     "Koenig, Christian" <Christian.Koenig@....com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Deucher, Alexander" <Alexander.Deucher@....com>
Subject: Re: [PATCH 0/4] x86/mm/cpa: Fix cpa-array TLB invalidation

On Fri, Nov 30, 2018 at 04:19:46PM +0000, StDenis, Tom wrote:
> NAK I get a failure in TTM on init with your x86/mm branch (see attached 
> dmesg).

So the good news is that with some additional self-tests I can trivially
reproduce this. The bad news is that an otherwise straight forward
cleanup seems to make CPA horribly mad at me.

And since we're somewhat late in the release cycle, I suppose we should
do the simple thing first, and then I can try and figure out this CPA
mess later.

So how about this relatively simple partial revert to sort the problem.

---
Subject: x86/mm/cpa: Fix cpa_flush_array() TLB invalidation

In commit:

  a7295fd53c39 ("x86/mm/cpa: Use flush_tlb_kernel_range()")

I misread the cpa array code and incorrectly used
tlb_flush_kernel_range(), resulting in missing TLB flushes and
consequent failures.

Instead do a full invalidate in this case -- for now.

Fixes: a7295fd53c39 ("x86/mm/cpa: Use flush_tlb_kernel_range()")
Reported-by: "StDenis, Tom" <Tom.StDenis@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/mm/pageattr.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index bac35001d896..61bc7d1800d7 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -285,20 +285,16 @@ static void cpa_flush_all(unsigned long cache)
 	on_each_cpu(__cpa_flush_all, (void *) cache, 1);
 }
 
-static bool __cpa_flush_range(unsigned long start, int numpages, int cache)
+static bool __inv_flush_all(int cache)
 {
 	BUG_ON(irqs_disabled() && !early_boot_irqs_disabled);
 
-	WARN_ON(PAGE_ALIGN(start) != start);
-
 	if (cache && !static_cpu_has(X86_FEATURE_CLFLUSH)) {
 		cpa_flush_all(cache);
 		return true;
 	}
 
-	flush_tlb_kernel_range(start, start + PAGE_SIZE * numpages);
-
-	return !cache;
+	return false;
 }
 
 static void cpa_flush_range(unsigned long start, int numpages, int cache)
@@ -306,7 +302,14 @@ static void cpa_flush_range(unsigned long start, int numpages, int cache)
 	unsigned int i, level;
 	unsigned long addr;
 
-	if (__cpa_flush_range(start, numpages, cache))
+	WARN_ON(PAGE_ALIGN(start) != start);
+
+	if (__inv_flush_all(cache))
+		return;
+
+	flush_tlb_kernel_range(start, start + PAGE_SIZE * numpages);
+
+	if (!cache)
 		return;
 
 	/*
@@ -332,7 +335,12 @@ static void cpa_flush_array(unsigned long baddr, unsigned long *start,
 {
 	unsigned int i, level;
 
-	if (__cpa_flush_range(baddr, numpages, cache))
+	if (__inv_flush_all(cache))
+		return;
+
+	flush_tlb_all();
+
+	if (!cache)
 		return;
 
 	/*