Fixed CC:kvmarm, Added: Alexander Graf, Fixed: my From: Replying to myself with additional information on each option Alex Bennée <alex.bennee@xxxxxxxxxx> writes: > Hi, > > I've almost finished the ARMv8 guest debug support but I have one > problem left to solve. userspace needs to know how many hardware debug > registers are available for GDB to use. This information is available > from the ID_AA64DFR0_EL1 register. Currently I abuse GET_ONE_REG to > fetch it's value however semantically this is poor as it's API is for > getting guest state not host state and they could theoretically have > different values. > > So far the options I've examined are: > > * KVM ioctl GET_ONE_REG(ID_AA64DFR0_EL1) Nope, guest state API > * ptrace(PTRACE_GETREGSET, NT_ARM_HW_WATCH) Nope, ptrace requires attachment and you can't attach to your own thread group. > * KVM ioctl KVM_GET_DEBUGREGS > > This is currently x86 only and looks like it's more aimed at debug > registers than capability stuff. Also I'm not sure what the state of > this ioctl is compared to KVM_SET_GUEST_DEBUG. Do these APIs overlap or > is one an older deprecated x86 only API? I'm minded to re-use this ioctl and define it for ARM as reading the host debug architecture state ID_AA64DFR0/1_EL1. Currently for x86 it's used for getting vcpu debug registers which on ARM is handled via the GET/SET one reg interface. > * Export the information via sysfs > > I suppose the correct canonical non-subsystem specific way to make this > information available it to expose the data in some sort of sysfs node? > However I don't see any existing sysfs structure for the CPU. I suspect this would get complicated depending on the architecture. > * Expand /proc/cpuinfo > > I suspect adding extra text to be badly parsed by userspace is just > horrid and unacceptable behaviour ;-) > > * Add another KVM ioctl? > > This would have the downside of being specific to KVM and of course > proliferating the API space again. So unless there are any objections my intention to re-use the existing API calls for ARM architectures. -- Alex Bennée -- 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
