On 21/10/2021 02:50, Bjorn Helgaas wrote:

[+cc Gong, author of d91525eb8ee6]

On Wed, Oct 20, 2021 at 11:16:38AM +0800, Xuesong Chen wrote:

quoted

On 20/10/2021 03:23, Bjorn Helgaas wrote:

quoted

On Tue, Oct 19, 2021 at 12:50:33PM +0800, Xuesong Chen wrote:

quoted

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I wish we could also include the matching MCFG info For x86, we
put something like this in the dmesg log, but I guess pci_mcfg.c
doesn't do this:

  PCI: MMCONFIG for domain 0000 [bus 00-7f] at [mem 0xf0000000-0xf7ffffff] (base 0xf0000000)

I can add the similar dmesg log in pci_mcfg.c to make it's
consistent between different arches

I think that might be nice.  It should probably be a separate patch
since it's not really related to the others.

Yes, will do.

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This patch will try to handle this case in a more common way instead of the
original 'arch' specific solution, which will be beneficial to all the
APEI-dependent platforms after that.

This actually doesn't say anything about what the patch does or how it
works.  It says "handles this case in a more common way" but with no
details.

Good suggestion, I'll give more details about that...

quoted

The EINJ table contains "injection instructions" that can read or
write "register regions" described by generic address structures (see
ACPI v6.3, sec 18.6.2 and 18.6.3), and __einj_error_trigger() requests
those register regions with request_mem_region() or request_region()
before executing the injections instructions.

IIUC, this patch basically says "if this region is part of the MCFG
area, we don't need to reserve it." That leads to the questions of why
we need to reserve *any* of the areas

AFAIK, the MCFG area is reserved since the ECAM module will provide
a generic Kernel Programming Interfaces(KPI), e.g,
pci_generic_config_read(...), so all the drivers are allowed to
access the pci config space only by those KPIs in a consistent and
safe way, direct raw access will break the rule.  Correct me if I am
missing sth.

quoted

and why it's safe to simply skip reserving regions that are part
of the MCFG area.

Actual there is a commit d91525eb8ee6("ACPI, EINJ: Enhance error
injection tolerance level") before to address this issue, the entire
commit log as below:

    Some BIOSes utilize PCI MMCFG space read/write opertion to trigger
    specific errors. EINJ will report errors as below when hitting such
    cases:
    
    APEI: Can not request [mem 0x83f990a0-0x83f990a3] for APEI EINJ Trigger registers
    
    It is because on x86 platform ACPI based PCI MMCFG logic has
    reserved all MMCFG spaces so that EINJ can't reserve it again.
    We already trust the ACPI/APEI code when using the EINJ interface
    so it is not a big leap to also trust it to access the right
    MMCFG addresses. Skip address checking to allow the access.

I'm not really convinced by that justification because I don't think
the issue here is *trust*.  If all we care about is trust, and we
trust the ACPI/APEI code, why do we need to reserve anything at all
when executing EINJ actions?

I think the resource reservation issue is about coordinating multiple
users of the address space.  A driver reserves the MMIO address space
of a device it controls so no other driver can reserve it at the same
time and cause conflicts.

I'm not really convinced by this mutual exclusion argument either,
because I haven't yet seen a situation where we say "EINJ needs a
resource that's already in use by somebody else, so we can't use
EINJ."  When conflicts arise, the response is always "we'll just
stop reserving this conflicting resource but use it anyway."

I think the only real value in apei_resources_request() is a little
bit of documentation in /proc/iomem.  For ERST and EINJ, even that
only lasts for the tiny period when we're actually executing an
action.

So convince me there's a reason why we shouldn't just remove
apei_resources_request() completely :)

I have to confess that currently I have no strong evidence/reason to convince
you that it's absolute safe to remove apei_resources_request(),  probably in
some conditions it *does* require to follow the mutual exclusion usage model.
The ECAM/MCFG maybe a special case not like other normal device driver, since
all its MCFG space has been reserved during the initialization. Anyway, it's
another topic and good point well worth discussing in the future.

From the patch set itself, I don't think it's a nice idea to make a dramatic
change regarding the apei_resources_request() part, I suggest to keep the original
rationale untouched and based on that to fix the real issue at hand in a more
generic way.

Any thought? If no objection, I plan to finalize the next version patch according
to the previous feedbacks and send it out for reviewing soon...

Thanks,
Xuesong

quoted

Except that the above explanation, IMO the EINJ is only a RAS debug
framework, in this code path, sometimes we need to acesss the
address within the MCFG space directly to trigger kind of HW error,
which behavior does not like the normal device driver's, in this
case some possible unsafe operations (bypass the ecam ops) can be
mitigated because the touched device will generate some HW errors
and the RAS handling part will preempt its corresponding drivers to
fix/log the HW error, that's my understanding about that.

quoted

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Signed-off-by: Xuesong Chen <redacted>
Reported-by: kernel test robot <redacted>
Reviewed-by: Lorenzo Pieralisi <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Rafael. J. Wysocki <rafael@kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Tomasz Nowicki <redacted>
---
 arch/x86/pci/mmconfig-shared.c | 28 --------------------------
 drivers/acpi/apei/apei-base.c  | 45 ++++++++++++++++++++++++++++--------------
 2 files changed, 30 insertions(+), 43 deletions(-)

diff --git a/arch/x86/pci/mmconfig-shared.c b/arch/x86/pci/mmconfig-shared.c
index 0b961fe6..12f7d96 100644
--- a/arch/x86/pci/mmconfig-shared.c
+++ b/arch/x86/pci/mmconfig-shared.c

@@ -605,32 +605,6 @@ static int __init pci_parse_mcfg(struct acpi_table_header *header)
 	return 0;
 }
 
-#ifdef CONFIG_ACPI_APEI
-extern int (*arch_apei_filter_addr)(int (*func)(__u64 start, __u64 size,
-				     void *data), void *data);
-
-static int pci_mmcfg_for_each_region(int (*func)(__u64 start, __u64 size,
-				     void *data), void *data)
-{
-	struct pci_mmcfg_region *cfg;
-	int rc;
-
-	if (list_empty(&pci_mmcfg_list))
-		return 0;
-
-	list_for_each_entry(cfg, &pci_mmcfg_list, list) {
-		rc = func(cfg->res.start, resource_size(&cfg->res), data);
-		if (rc)
-			return rc;
-	}
-
-	return 0;
-}
-#define set_apei_filter() (arch_apei_filter_addr = pci_mmcfg_for_each_region)
-#else
-#define set_apei_filter()
-#endif
-
 static void __init __pci_mmcfg_init(int early)
 {
 	pci_mmcfg_reject_broken(early);

@@ -665,8 +639,6 @@ void __init pci_mmcfg_early_init(void)
 		else
 			acpi_table_parse(ACPI_SIG_MCFG, pci_parse_mcfg);
 		__pci_mmcfg_init(1);
-
-		set_apei_filter();
 	}
 }
 

diff --git a/drivers/acpi/apei/apei-base.c b/drivers/acpi/apei/apei-base.c
index c7fdb12..daae75a 100644
--- a/drivers/acpi/apei/apei-base.c
+++ b/drivers/acpi/apei/apei-base.c

@@ -21,6 +21,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/init.h>
+#include <linux/pci.h>
 #include <linux/acpi.h>
 #include <linux/slab.h>
 #include <linux/io.h>

@@ -448,13 +449,34 @@ static int apei_get_nvs_resources(struct apei_resources *resources)
 	return acpi_nvs_for_each_region(apei_get_res_callback, resources);
 }
 
-int (*arch_apei_filter_addr)(int (*func)(__u64 start, __u64 size,
-				     void *data), void *data);
-static int apei_get_arch_resources(struct apei_resources *resources)
+#ifdef CONFIG_PCI
+extern struct list_head pci_mmcfg_list;
+static int apei_filter_mcfg_addr(struct apei_resources *res,
+			struct apei_resources *mcfg_res)
+{
+	int rc = 0;
+	struct pci_mmcfg_region *cfg;
+
+	if (list_empty(&pci_mmcfg_list))
+		return 0;
+
+	apei_resources_init(mcfg_res);
+	list_for_each_entry(cfg, &pci_mmcfg_list, list) {
+		rc = apei_res_add(&mcfg_res->iomem, cfg->res.start, resource_size(&cfg->res));
+		if (rc)
+			return rc;
+	}
 
+	/* filter the mcfg resource from current APEI's */
+	return apei_resources_sub(res, mcfg_res);
+}
+#else
+static inline int apei_filter_mcfg_addr(struct apei_resources *res,
+			struct apei_resources *mcfg_res)
 {
-	return arch_apei_filter_addr(apei_get_res_callback, resources);
+	return 0;
 }
+#endif
 
 /*
  * IO memory/port resource management mechanism is used to check

@@ -486,15 +508,9 @@ int apei_resources_request(struct apei_resources *resources,
 	if (rc)
 		goto nvs_res_fini;
 
-	if (arch_apei_filter_addr) {
-		apei_resources_init(&arch_res);
-		rc = apei_get_arch_resources(&arch_res);
-		if (rc)
-			goto arch_res_fini;
-		rc = apei_resources_sub(resources, &arch_res);
-		if (rc)
-			goto arch_res_fini;
-	}
+	rc = apei_filter_mcfg_addr(resources, &arch_res);
+	if (rc)
+		goto arch_res_fini;
 
 	rc = -EINVAL;
 	list_for_each_entry(res, &resources->iomem, list) {

@@ -544,8 +560,7 @@ int apei_resources_request(struct apei_resources *resources,
 		release_mem_region(res->start, res->end - res->start);
 	}
 arch_res_fini:
-	if (arch_apei_filter_addr)
-		apei_resources_fini(&arch_res);
+	apei_resources_fini(&arch_res);
 nvs_res_fini:
 	apei_resources_fini(&nvs_resources);
 	return rc;

-- 
1.8.3.1

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