Avi Kivity wrote: > Jan Kiszka wrote: >> Hi, >> >> turning on MMU_DEBUG and AUDIT in arch/x86/kvm/mmu.c (and fixing a build >> error, patch will follow) I got this (and then a #GP :( - patch will >> follow): >> >> ... >> kvm_mmu_get_page: looking gfn 0 role f0120 >> kvm_mmu_get_page: found >> kvm_mmu_get_page: looking gfn 0 role f0220 >> kvm_mmu_get_page: found >> kvm_mmu_get_page: looking gfn 0 role f0320 >> kvm_mmu_get_page: found >> kvm_mmu_get_page: looking gfn e1f role e0044 >> kvm_mmu_get_page: adding gfn e1f role e0044 >> rmap_write_protect: spte ffff8100660a60f8 7ca98067 >> paging64_page_fault: addr 100105 err 19 >> audit_write_protection: (pre page fault) shadow page has writable >> mappings: gfn e1f role e0044 >> audit: (pre page fault) nontrapping pte in nonleaf level: levels 4 gva >> 8000000000 level 4 pte 0 >> >> Is the last message indicating a problem? I get it very early during >> guest boot. oos_shadow is disabled. >> > > Yes. It means the guest will receive a page fault if is accesses > anything this pte points to. Theoretically we could have made this > work, but we never did. > > But the message is self-contradictory. Level 4 PTEs map 0.5TB each, and > the gva mentioned isn't 0.5TB aligned. > >> I'm currently trying to understand an obvious inconsistency in the pte >> describing a page of the virtio-net rx ring. On some guests with some >> qemu (upstream) command lines I can trigger this with '-smb /some/path' >> and then doing smbclient -L in the guest. Once the inconsistency slipped >> in, host and guest see different page contents and virtio-net stops to >> work. Very strange, but fortunately easily reproducible here. Any hints >> or debugging suggestions welcome! >> > > What type of inconsistency? pfn or flags? > The former. Here is a before-after walk of the shadow and the host page table (format: <entry address> (<entry value>) ): [good] gva=ffff88001ef22000: 000000002fc57000 -> 000000002fc57880 (000000003d119027) -> 000000003d119000 (000000005d9bf027) -> 000000005d9bf7b8 (000000003d159027) -> 000000003d159910 (000000002fbce063) -> 000000002fbce000 = 01 00 07 00 hva=00007f4665cac000: 00000000701f4000 -> 00000000701f47f0 (000000005d925067) -> 000000005d9258c8 (000000005d8c5067) -> 000000005d8c5970 (000000003d2b4067) -> 000000003d2b4560 (800000002fbce067) -> 800000002fbce000 = 01 00 07 00 [bad] gva=ffff88001ef22000: 000000002fc57000 -> 000000002fc57880 (000000003d119027) -> 000000003d119000 (000000005d9bf027) -> 000000005d9bf7b8 (000000003d159027) -> 000000003d159910 (000000002fbce063) -> 000000002fbce000 = 01 00 0a 00 hva=00007f4665cac000: 00000000701f4000 -> 00000000701f47f0 (000000005d925067) -> 000000005d9258c8 (000000005d8c5067) -> 000000005d8c5970 (000000003d2b4067) -> 000000003d2b4560 (800000006576d067) -> 800000006576d000 = 01 00 10 00 That raise a question for a kvm-mmu newbie like me: If a page of the qemu process gets pushed around (here likely due to fork()->exec(smbd)->COW), how will kvm's shadow table catch up? Via MMU_NOTIFIER? I'm on a 2.6.25 kernel, and that means without CONFIG_MMU_NOTIFIER. So far I assumed that kernels without this feature do not work optimally, but they won't break my guests... Jan
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