1) when passthrough some pcie device, such as AMD gpus,
kvm will report:"Unsupported FSC:" err.
2) the main reason is kvm setting memory type to
PAGE_S2_DEVICE(DEVICE_nGnRE), but in guestos, all of device io memory
type when ioremapping (including gpu driver TTM memory type) is
setting to MT_NORMAL_NC.
3) according to ARM64 stage1&stage2 conbining rules.
memory type attributes combining rules:
Normal-WB < Normal-WT < NormalNC < Device-GRE < Device-nGRE <
DevicenGnRE < Device-nGnRnE
Normal-WB is weakest,Device-nGnRnE is strongest.
refferring to 'Arm Architecture Reference Manual Armv8,
for Armv8-A architecture profile' pdf, chapter B2.8
refferring to 'ARM System Memory Management Unit Architecture
Specification SMMU architecture version 3.0 and version 3.1' pdf,
chapter 13.1.5
4) therefore, the I/O memory attribute of the VM is setting to
DevicenGnRE is a big mistake. it causes all device memory accessing in
the virtual machine must be aligned.
To summarize: stage2 memory type cannot be stronger than stage1 in
arm64 archtechture.
Signed-off-by: xieming <xieming@xxxxxxxxxx>
---
virt/kvm/arm/mmu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 11103b75c596..9b7fb13f4546 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1209,7 +1209,7 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
pfn = __phys_to_pfn(pa);
for (addr = guest_ipa; addr < end; addr += PAGE_SIZE) {
- pte_t pte = pfn_pte(pfn, PAGE_S2_DEVICE);
+ pte_t pte = pfn_pte(pfn, PAGE_S2);
if (writable)
pte = kvm_s2pte_mkwrite(pte);
--
2.27.0
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