Re: [RFC 0/2] x86/PCI: Ignore EFI memmap MMIO entries

[Hans de Goede]

Hi All,

On 2/14/22 16:17, Hans de Goede wrote:
> Hi All,
> 
> Here is a new attempt at fixing the issue where on some laptops
> there are EFI memmap MMIO entries covering the entire PCI bridge
> mem window, causing Linux to be unable to find free space to
> assign to unassigned BARs.
> 
> This is marked as RFC atm because I'm waiting for feedback from
> testers.

Unfortunately the troublesome 0xdfa00000-0xdfa0ffff region on
the Lenovo X1 carbon gen 2 is marked as MMIO by the EFI memmap,
so the approach from this series won't work.

Interestingly enough this RFC series does seem to help to fix
the suspend/resume on this x1c2, since for some reason merely
splitting the original:

BIOS-e820: [mem 0x00000000dceff000-0x00000000dfa0ffff] reserved

range into:

BIOS-e820: [mem 0x00000000dceff000-0x00000000df9fffff] reserved
BIOS-e820: [mem 0x00000000dfa00000-0x00000000dfa0ffff] MMIO

causes the PCI resource allocation code to pick slightly
different resources avoiding the troublesome overlap, see:
https://bugzilla.redhat.com/show_bug.cgi?id=2029207
for logs.

But I don't think we should rely in this, since from a
arch_remove_reservations() pov the troublesome overlap area
which is now marked as MMIO is fair game for PCI bars with
the change to allow MMIO areas for PCI bars, so things seem
to mostly work by sheer luck after this RFC series.

So now I have yet another plan to fix this (see below) I'll get
that tested and assuming it works post that as a proper patch.

Regards,

Hans



diff --git a/arch/x86/include/asm/pci_x86.h b/arch/x86/include/asm/pci_x86.h
index 490411dba438..573e1323f490 100644
--- a/arch/x86/include/asm/pci_x86.h
+++ b/arch/x86/include/asm/pci_x86.h
@@ -64,6 +64,8 @@ void pcibios_scan_specific_bus(int busn);
 
 /* pci-irq.c */
 
+struct pci_dev;
+
 struct irq_info {
 	u8 bus, devfn;			/* Bus, device and function */
 	struct {
@@ -232,3 +234,9 @@ static inline void mmio_config_writel(void __iomem *pos, u32 val)
 # define x86_default_pci_init_irq	NULL
 # define x86_default_pci_fixup_irqs	NULL
 #endif
+
+#if defined CONFIG_PCI && defined CONFIG_ACPI
+extern bool pci_use_e820;
+#else
+#define pci_use_e820 true
+#endif
diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
index 9b9fb7882c20..e8dc9bc327bd 100644
--- a/arch/x86/kernel/resource.c
+++ b/arch/x86/kernel/resource.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/ioport.h>
 #include <asm/e820/api.h>
+#include <asm/pci_x86.h>
 
 static void resource_clip(struct resource *res, resource_size_t start,
 			  resource_size_t end)
@@ -28,6 +29,9 @@ static void remove_e820_regions(struct resource *avail)
 	int i;
 	struct e820_entry *entry;
 
+	if (!pci_use_e820)
+		return;
+
 	for (i = 0; i < e820_table->nr_entries; i++) {
 		entry = &e820_table->entries[i];
 
diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index 052f1d78a562..7167934819b3 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/efi.h>
 #include <linux/pci.h>
 #include <linux/acpi.h>
 #include <linux/init.h>
@@ -21,6 +22,7 @@ struct pci_root_info {
 
 static bool pci_use_crs = true;
 static bool pci_ignore_seg;
+bool pci_use_e820 = true;
 
 static int __init set_use_crs(const struct dmi_system_id *id)
 {
@@ -291,6 +293,28 @@ static bool resource_is_pcicfg_ioport(struct resource *res)
 		res->start == 0xCF8 && res->end == 0xCFF;
 }
 
+static bool resource_matches_efi_mmio_region(const struct resource *res)
+{
+	unsigned long long start, end;
+	efi_memory_desc_t *md;
+
+	if (!efi_enabled(EFI_MEMMAP))
+		return false;
+
+	for_each_efi_memory_desc(md) {
+		if (md->type != EFI_MEMORY_MAPPED_IO)
+			continue;
+
+		start = md->phys_addr;
+		end = start + (md->num_pages << EFI_PAGE_SHIFT) - 1;
+
+		if (res->start >= start && res->end <= end)
+			return true;
+	}
+
+	return false;
+}
+
 static int pci_acpi_root_prepare_resources(struct acpi_pci_root_info *ci)
 {
 	struct acpi_device *device = ci->bridge;
@@ -300,9 +324,16 @@ static int pci_acpi_root_prepare_resources(struct acpi_pci_root_info *ci)
 
 	status = acpi_pci_probe_root_resources(ci);
 	if (pci_use_crs) {
-		resource_list_for_each_entry_safe(entry, tmp, &ci->resources)
+		resource_list_for_each_entry_safe(entry, tmp, &ci->resources) {
 			if (resource_is_pcicfg_ioport(entry->res))
 				resource_list_destroy_entry(entry);
+			if (resource_matches_efi_mmio_region(entry->res)) {
+				dev_info(&device->dev,
+					"host bridge window %pR is marked by EFI as MMIO\n",
+					entry->res);
+				pci_use_e820 = false;
+			}
+		}
 		return status;
 	}