linux-kernel - Re: [PATCH] x86, acpi: Handle lapic/x2apic entries in MADT

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Date:	Wed, 26 Aug 2015 13:43:09 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	"Anaczkowski, Lukasz" <lukasz.anaczkowski@...el.com>
CC:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"Brown, Len" <len.brown@...el.com>, "pavel@....cz" <pavel@....cz>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH] x86, acpi: Handle lapic/x2apic entries in MADT

On 26/08/15 12:42, Lorenzo Pieralisi wrote:
> Hi Lukasz,
> 
> On Wed, Aug 26, 2015 at 11:43:04AM +0100, Marc Zyngier wrote:
>> Hi Lukasz,
>>
>> On 26/08/15 08:04, Anaczkowski, Lukasz wrote:
>>> On Monday, August 3, 2015 8:26 PM
>>> Lukasz Anaczkowski <lukasz.anaczkowski@...el.com> wrote:
>>>
>>>> v2: Fixed ARM64 syntax error
>>>
>>> Hi Marc,
>>>
>>> Does this patch look ok now?
> 
> No it does not, it seems to break arm64, I put together a fix
> below. I do not think the way you handle the count increment
> in acpi_parse_entries() is correct anyway, since you increment
> it only if max_entries != 0, which changes mainline behaviour.

Yeah, this is fundamentally flawed:

- count is only incremented when max_entries != 0, as you noticed
- With max_entries != 0, count now represent the sum of all matches
  Is that expected?
- The proc iteration stops after the first match. Why?
- The test for max_entries is done inside the proc loop. Why?

I came up with the following patch that restores arm64 to a booting state.

If the intention was to change the meaning of the acpi_parse_entries
return value, then this should be documented and agreed upon.

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 1217e41..f06327f 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -249,19 +249,24 @@ acpi_parse_entries(char *id, unsigned long table_size,

 	while (((unsigned long)entry) + sizeof(struct acpi_subtable_header) <
 	       table_end) {
+		bool match = false;
+
+		if (max_entries && count >= max_entries)
+			break;
 		for (i = 0; i < proc_num; i++) {
 			if (entry->type != proc[i].id)
 				continue;
-			if (max_entries && count++ >= max_entries)
-				continue;
 			if (proc[i].handler(entry, table_end)) {
 				proc[i].count = -EINVAL;
 				return -EINVAL;
 			}
 			proc[i].count++;
-			break;
+			match = true;
 		}

+		if (match)
+			count++;
+
 		/*
 		 * If entry->length is 0, break from this loop to avoid
 		 * infinite loop.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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