KVM: pci passthrough un-page-aligned mmio device on machines w/o VT-d
PATCH 1/3 KVM: pci passthrough un-page-aligned mmio device on machines w/o VT-d
the following patches apply to KVM-79. however, just now I viewed the code in KVM-81, and saw the problem remains.
when assigning a pci device to guest os, the qemu can not guarantee the device's virtual iomem address has the same page offset with the real one. for example: in native linux, the the starting iomem address for my via-rhine nic is 0x00000000df9fff00, which is not page aligned. But QEMU will emulate this nic has a page aligned mmio address. This difference will make guest os access the wrong address when it tries to do mmio.
It seems Han Weidong has disabled QEMU assign this kinds of devices to guest os. The following patch will remove this constraint.
---
diff -uNr kvm-79/bios/rombios32.c kvm-79-fixed/bios/rombios32.c
bios/rombios32.c 2008-12-12 11:38:41.000000000 +0800 renamed from bios/rombios32.c 2008-11-12 19:48:01.000000000 +0800 +3 -1
@@ -931,7 +931,9 @@ paddr = &pci_bios_bigmem_addr; else paddr = &pci_bios_mem_addr; - *paddr = (*paddr + size - 1) & ~(size - 1); + + /* To preserve the iomem page offset. --Xiaojian Liu */ + *paddr = ((*paddr + size - 1) & ~(size - 1)) | (val & 0x0fff); pci_set_io_region_addr(d, i, *paddr); *paddr += size; }
Xiaojian Liu
Quoted 12 lines · 刘晓建
the following patches apply to KVM-79. however, just now I viewed the code in KVM-81, and saw the problem remains.
when assigning a pci device to guest os, the qemu can not guarantee the device's virtual iomem address has the same page offset with the real one.
for example: in native linux, the the starting iomem address for my via-rhine nic is0x00000000df9fff00, which is not page aligned. But QEMU will emulate this nic has a page aligned mmio address. This difference will make guest os access the wrong address when it tries to do mmio.
Pls note that multiple devices may share one page for their MMIO, and they may be assigned to different guests, there is potential isolation issue. So we don't allow to assign these devices.
Regards,
Weidong
Quoted 19 lines
It seems Han Weidong has disabled QEMU assign this kinds of devices to guest os. The following patch will remove this constraint.
---
diff -uNrkvm-79/bios/rombios32.ckvm-79-fixed/bios/rombios32.cbios/rombios32.c 2008-12-12 11:38:41.000000000 +0800 renamed from bios/rombios32.c 2008-11-12 19:48:01.000000000 +0800 +3
-1@@ -931,7 +931,9 @@ paddr = &pci_bios_bigmem_addr; else paddr = &pci_bios_mem_addr; - *paddr = (*paddr + size - 1) & ~(size - 1); + + /* To preserve the iomem page offset. --Xiaojian Liu */ + *paddr = ((*paddr + size - 1) & ~(size - 1)) | (val & 0x0fff); pci_set_io_region_addr(d, i, *paddr); *paddr += size; }Xiaojian Liu