Re: [PULL v2 75/86] include/hw/pci/pcie_host: Correct PCIE_MMCFG_SIZE_MAX

[Michael S. Tsirkin]

On Thu, May 26, 2022 at 09:34:08PM +0200, BALATON Zoltan wrote:
> On Thu, 26 May 2022, Michael S. Tsirkin wrote:
> > On Thu, May 26, 2022 at 06:43:25PM +0200, BALATON Zoltan wrote:
> > > On Thu, 26 May 2022, BALATON Zoltan wrote:
> > > > Hello,
> > > > 
> > > > On Thu, 26 May 2022, Daniel Henrique Barboza wrote:
> > > > > Hi,
> > > > > 
> > > > > This patch broke the boot of the sam460ex ppc machine:
> > > > > 
> > > > > qemu-system-ppc -M sam460ex -kernel
> > > > > ./buildroot/qemu_ppc_sam460ex-latest/vmlinux \
> > > > > -device virtio-net-pci,netdev=net0 -netdev user,id=net0 -serial 
> > > > > mon:stdio \
> > > > > -nographic -snapshot
> > > > > qemu-system-ppc: ../hw/pci/pcie_host.c:97: pcie_host_mmcfg_init:
> > > > > Assertion `size <= PCIE_MMCFG_SIZE_MAX' failed.
> > > 
> > > With just qemu-system-ppc -M sam460ex the assert seems to happen when the
> > > guest (board firmware?) writes a value to CFGMSK reg:
> > > 
> > > (gdb) bt
> > > #0  0x00007ffff68ff4a0 in raise () at /lib64/libc.so.6
> > > #1  0x00007ffff68ea536 in abort () at /lib64/libc.so.6
> > > #2  0x00007ffff68ea42f in _nl_load_domain.cold () at /lib64/libc.so.6
> > > #3  0x00007ffff68f7ed2 in  () at /lib64/libc.so.6
> > > #4  0x000055555596646f in pcie_host_mmcfg_init (e=e@entry=0x5555567942f0, 
> > > size=size@entry=0x20000000) at ../hw/pci/pcie_host.c:97
> > > #5  0x000055555596653b in pcie_host_mmcfg_map (size=0x20000000, 
> > > addr=0xd20000000, e=0x5555567942f0) at ../hw/pci/pcie_host.c:105
> > > #6  pcie_host_mmcfg_update (e=0x5555567942f0, enable=0x1, 
> > > addr=0xd20000000, size=0x20000000) at ../hw/pci/pcie_host.c:118
> > > #7  0x0000555555a70d7c in ppc_dcr_write (dcr_env=0x555556669c10, 
> > > dcrn=0x122, val=0xe0000001) at ../hw/ppc/ppc.c:1418
> > > #8  0x0000555555abdabb in helper_store_dcr (env=0x555556633360, 
> > > dcrn=0x122, val=0xe0000001) at ../target/ppc/timebase_helper.c:188
> > > 
> > > This is done in the board firmware here:
> > > 
> > > https://git.qemu.org/?p=u-boot-sam460ex.git;a=blob;f=arch/powerpc/cpu/ppc4xx/4xx_pcie.c;h=13348be93dccc74c13ea043d6635a7f8ece4b5f0;hb=HEAD#l963
> > > 
> > > when trying to map config space. Here the size is calculated as 0x20000000
> > > which does not fit the assert. I'm not sure what this means though and 
> > > where
> > > is the problem. Any ideas?
> > > 
> > > Regards,
> > > BALATON Zoltan
> > 
> > 
> > It says so, does it not?
> > 
> > 1051         switch (port) {
> > 1052         case 0:
> > 1053                 mtdcr(DCRN_PEGPL_CFGBAH(PCIE0), high);
> > 1054                 mtdcr(DCRN_PEGPL_CFGBAL(PCIE0), low);
> > 1055                 mtdcr(DCRN_PEGPL_CFGMSK(PCIE0), 0xe0000001); /* 512MB 
> > region, valid */
> > 1056                 break;
> > 1057         case 1:
> > 1058                 mtdcr(DCRN_PEGPL_CFGBAH(PCIE1), high);
> > 1059                 mtdcr(DCRN_PEGPL_CFGBAL(PCIE1), low);
> > 1060                 mtdcr(DCRN_PEGPL_CFGMSK(PCIE1), 0xe0000001); /* 512MB 
> > region, valid */
> > 1061                 break;
> > 1062 #if CONFIG_SYS_PCIE_NR_PORTS > 2
> > 1063         case 2:
> > 1064                 mtdcr(DCRN_PEGPL_CFGBAH(PCIE2), high);
> > 1065                 mtdcr(DCRN_PEGPL_CFGBAL(PCIE2), low);
> > 1066                 mtdcr(DCRN_PEGPL_CFGMSK(PCIE2), 0xe0000001); /* 512MB 
> > region, valid */
> > 1067                 break;
> > 1068 #endif
> 
> Yes, the size matches what the firmware programs it.
> 
> > and basically according to spec max size is 256MB.
> 
> Maybe this SoC does not follow the spec you're referring to? Complies to
> some other spec like a newer version or has its own idea? I don't have docs
> to tell.
> 
> > we can fix the firmware of course, or we can just drop the assert,
> > or force it within range in the ppc code.
> 
> According to this random Cisco IOS dump I've found:
> 
> https://www.hardware.com.br/comunidade/switch-cisco/1128380/
> 
> looks like this value is valid on that hardware so that likely means we
> should not "fix" the firmware. (Also not because it's what the real board
> uses or at least very close to it so it should work with the emulated board
> too and keeping it close to the real hardware ensures the emulation is
> accurate.) That means we should either revert this back (why was this
> changed back in the first place, did it cause any problems?) or maybe try
> restricting the value in the PPC model.

It didn't it was just weird behaviour. High bit in the address was
ignored, so the config space was mapped many times at offsets
0,256M, etc up to whatever size was.
> > Fixing firmware seems cleaner ... want to try?
> > Any preference?
> 
> I'd leave making a patch to someone else but can help testing it. As per the
> above if we can't revert it maybe we can try restricting size in ppc440_uc.c
> where pcie_host_mmcfg_update() is called. Since the PCIe bus on this board
> probably does not work now anyway probably nothing will notice this for now.
> 
> Regards,
> BALATON Zoltan


I am guessing the unused space is just ignored.
so I am inclined to restrict in PPC model,
where we also have a chance to document what is going on.




diff --git a/hw/ppc/ppc440_uc.c b/hw/ppc/ppc440_uc.c
index 993e3ba955..a1ecf6dd1c 100644
--- a/hw/ppc/ppc440_uc.c
+++ b/hw/ppc/ppc440_uc.c
@@ -1180,6 +1180,14 @@ static void dcr_write_pcie(void *opaque, int dcrn, 
uint32_t val)
     case PEGPL_CFGMSK:
         s->cfg_mask = val;
         size = ~(val & 0xfffffffe) + 1;
+        /*
+         * Firmware sets this register to E0000001. Why we are not sure,
+         * but the current guess is anything above PCIE_MMCFG_SIZE_MAX is
+         * ignored.
+         */
+        if (size > PCIE_MMCFG_SIZE_MAX) {
+            size = PCIE_MMCFG_SIZE_MAX;
+        }
         pcie_host_mmcfg_update(PCIE_HOST_BRIDGE(s), val & 1, s->cfg_base, 
size);
         break;
     case PEGPL_MSGBAH: