Re: [SeaBIOS] [PATCH v5] limit physical address space size

From: Gerd Hoffmann <kraxel@redhat.com>
To: Claudio Fontana <cfontana@suse.de>
Cc: Kevin O'Connor <kevin@koconnor.net>,
	 Peter Maydell <peter.maydell@linaro.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	seabios@seabios.org, qemu-devel@nongnu.org
Subject: Re: [SeaBIOS] [PATCH v5] limit physical address space size
Date: Fri, 10 Nov 2023 12:04:24 +0100	[thread overview]
Message-ID: <iqerqemhgokkgemaxnfktoz6ssrk3uqc4bncoghmhhxaaycleo@u5k642niiya3> (raw)
In-Reply-To: <npmimli5x4vcwxb3csaaut3sobuzsex7pgtf4xbrbnfd22hnyz@ixh5tmn4xkpk>

  Hi,

> This only changes the placement of the PCI bars.  The pci setup code is
> the only consumer of that variable, guess it makes sense to move the
> quirk to the pci code (as suggested by Kevin) to clarify this.

i.e. like this:

From d538dc7d4316e557ae302464252444d09de0681d Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Tue, 7 Nov 2023 13:49:31 +0100
Subject: [PATCH] limit physical address space size

For better compatibility with old linux kernels,
see source code comment.

Related (same problem in ovmf):
https://github.com/tianocore/edk2/commit/c1e853769046

Reported-by: Claudio Fontana <cfontana@suse.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 src/fw/pciinit.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
index c7084f5e397e..7aeea61bfd05 100644
--- a/src/fw/pciinit.c
+++ b/src/fw/pciinit.c
@@ -52,6 +52,7 @@ u64 pcimem64_start = BUILD_PCIMEM64_START;
 u64 pcimem64_end   = BUILD_PCIMEM64_END;
 u64 pci_io_low_end = 0xa000;
 u32 pci_use_64bit  = 0;
+u32 pci_phys_bits  = 0;
 
 struct pci_region_entry {
     struct pci_device *dev;
@@ -967,7 +968,7 @@ static int pci_bios_check_devices(struct pci_bus *busses)
             if (hotplug_support == HOTPLUG_PCIE)
                 resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
             if (hotplug_support && pci_use_64bit && is64 && (type == PCI_REGION_TYPE_PREFMEM))
-                align = (u64)1 << (CPUPhysBits - 11);
+                align = (u64)1 << (pci_phys_bits - 11);
             if (align > sum && hotplug_support && !resource_optional)
                 sum = align; /* reserve min size for hot-plug */
             if (size > sum) {
@@ -1131,12 +1132,12 @@ static void pci_bios_map_devices(struct pci_bus *busses)
         r64_mem.base = le64_to_cpu(romfile_loadint("etc/reserved-memory-end", 0));
         if (r64_mem.base < 0x100000000LL + RamSizeOver4G)
             r64_mem.base = 0x100000000LL + RamSizeOver4G;
-        if (CPUPhysBits) {
-            u64 top = 1LL << CPUPhysBits;
+        if (pci_phys_bits) {
+            u64 top = 1LL << pci_phys_bits;
             u64 size = (ALIGN(sum_mem, (1LL<<30)) +
                         ALIGN(sum_pref, (1LL<<30)));
             if (pci_use_64bit)
-                size = ALIGN(size, (1LL<<(CPUPhysBits-3)));
+                size = ALIGN(size, (1LL<<(pci_phys_bits-3)));
             if (r64_mem.base < top - size) {
                 r64_mem.base = top - size;
             }
@@ -1181,8 +1182,16 @@ pci_setup(void)
 
     dprintf(3, "pci setup\n");
 
-    if (CPUPhysBits >= 36 && CPULongMode && RamSizeOver4G)
+    if (CPUPhysBits >= 36 && CPULongMode && RamSizeOver4G) {
         pci_use_64bit = 1;
+        pci_phys_bits = CPUPhysBits;
+        if (pci_phys_bits > 46) {
+            // Old linux kernels have trouble dealing with more than 46
+            // phys-bits, so avoid that for now.  Seems to be a bug in the
+            // virtio-pci driver.  Reported: centos-7, ubuntu-18.04
+            pci_phys_bits = 46;
+        }
+    }
 
     dprintf(1, "=== PCI bus & bridge init ===\n");
     if (pci_probe_host() != 0) {
-- 
2.41.0


