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

[Kevin O'Connor]

On Fri, Nov 10, 2023 at 12:04:24PM +0100, Gerd Hoffmann wrote:
> 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 
> 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 
> Signed-off-by: Gerd Hoffmann
>
> 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;

FWIW, all these flags are getting a bit confusing.  Maybe do something
like the patch below.
> 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) {

FYI, this is a change in behavior - previously this condition would
have been taken even if CPULongMode or RamSizeOver4G is false.  I'm
not sure if this change is intentional.  (My example patch below
follows your lead here.)
>        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) {

Possible alternate variable naming:

diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
index c7084f5..cd64d6e 100644
--- a/src/fw/pciinit.c
+++ b/src/fw/pciinit.c
@@ -46,12 +46,16 @@ static const char *region_type_name[] = {
     [ PCI_REGION_TYPE_PREFMEM ] = "prefmem",
 };

+// Memory ranges exported to legacy ACPI type table generation
 u64 pcimem_start   = BUILD_PCIMEM_START;
 u64 pcimem_end     = BUILD_PCIMEM_END;
 u64 pcimem64_start = BUILD_PCIMEM64_START;
 u64 pcimem64_end   = BUILD_PCIMEM64_END;
-u64 pci_io_low_end = 0xa000;
-u32 pci_use_64bit  = 0;
+
+// Memory resource allocation tracking
+static u64 pci_io_low_end = 0xa000;
+static u32 pci_use_64bit  = 0;
+static u64 pci_mem64_top  = 0;

struct pci_region_entry {
     struct pci_device *dev;
@@ -966,8 +970,9 @@ static int pci_bios_check_devices(struct pci_bus *busses)
             int resource_optional = 0;
             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);
+            if (hotplug_support && pci_use_64bit && is64
+                && (type == PCI_REGION_TYPE_PREFMEM))
+                align = pci_mem64_top >> 11;
             if (align > sum && hotplug_support && !resource_optional)
                 sum = align; /* reserve min size for hot-plug */
             if (size > sum) {
@@ -1131,14 +1136,13 @@ 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_mem64_top) {
             u64 size = (ALIGN(sum_mem, (1LL<<30)) +
                         ALIGN(sum_pref, (1LL<<30)));
             if (pci_use_64bit)
-                size = ALIGN(size, (1LL<<(CPUPhysBits-3)));
-            if (r64_mem.base < top - size) {
-                r64_mem.base = top - size;
+                size = ALIGN(size, pci_mem64_top >> 3);
+            if (r64_mem.base < pci_mem64_top - size) {
+                r64_mem.base = pci_mem64_top - size;
             }
             if (e820_is_used(r64_mem.base, size))
                 r64_mem.base -= size;
@@ -1181,8 +1185,16 @@ pci_setup(void)

dprintf(3, "pci setup\n");

-    if (CPUPhysBits >= 36 && CPULongMode && RamSizeOver4G)
+    if (CPUPhysBits >= 36 && CPULongMode && RamSizeOver4G) {
         pci_use_64bit = 1;
+        pci_mem64_top = 1LL << CPUPhysBits;
+        if (CPUPhysBits > 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_mem64_top = 1LL << 46;
+        }
+    }

dprintf(1, "=== PCI bus & bridge init ===\n");
     if (pci_probe_host() != 0) {

Cheers,
-Kevin