On 10/22/2012 05:16 PM, Gleb Natapov wrote: > On Fri, Oct 19, 2012 at 03:37:32PM +0800, Xiao Guangrong wrote: >> After commit b3356bf0dbb349 (KVM: emulator: optimize "rep ins" handling), >> the pieces of io data can be collected and write them to the guest memory >> or MMIO together. >> >> Unfortunately, kvm splits the mmio access into 8 bytes and store them to >> vcpu->mmio_fragments. If the guest uses "rep ins" to move large data, it >> will cause vcpu->mmio_fragments overflow >> >> The bug can be exposed by isapc (-M isapc): >> >> [23154.818733] general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC >> [ ......] >> [23154.858083] Call Trace: >> [23154.859874] [<ffffffffa04f0e17>] kvm_get_cr8+0x1d/0x28 [kvm] >> [23154.861677] [<ffffffffa04fa6d4>] kvm_arch_vcpu_ioctl_run+0xcda/0xe45 [kvm] >> [23154.863604] [<ffffffffa04f5a1a>] ? kvm_arch_vcpu_load+0x17b/0x180 [kvm] >> >> >> Actually, we can use one mmio_fragment to store a large mmio access for the >> mmio access is always continuous then split it when we pass the mmio-exit-info >> to userspace. After that, we only need two entries to store mmio info for >> the cross-mmio pages access >> > I wonder can we put the data into coalesced mmio buffer instead of If we put all mmio data into coalesced buffer, we should: - ensure the userspace program uses KVM_REGISTER_COALESCED_MMIO to register all mmio regions. - even if the MMIO region is not used by emulated-device, it also need to be registered. It will breaks old version userspace program. > exiting for each 8 bytes? Is it worth the complexity? Simpler way is always better but i failed, so i appreciate your guys comments. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
