From: James Hogan Date: Thu, 29 May 2014 09:16:35 +0000 (+0100) Subject: MIPS: KVM: Rewrite count/compare timer emulation X-Git-Tag: omap-for-v3.16/fixes-against-rc1~39^2~8^2~12 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e30492bbe95a2495930aa7db7eacde5141e45332;p=pandora-kernel.git MIPS: KVM: Rewrite count/compare timer emulation Previously the emulation of the CPU timer was just enough to get a Linux guest running but some shortcuts were taken: - The guest timer interrupt was hard coded to always happen every 10 ms rather than being timed to when CP0_Count would match CP0_Compare. - The guest's CP0_Count register was based on the host's CP0_Count register. This isn't very portable and fails on cores without a CP_Count register implemented such as Ingenic XBurst. It also meant that the guest's CP0_Cause.DC bit to disable the CP0_Count register took no effect. - The guest's CP0_Count register was emulated by just dividing the host's CP0_Count register by 4. This resulted in continuity problems when used as a clock source, since when the host CP0_Count overflows from 0x7fffffff to 0x80000000, the guest CP0_Count transitions discontinuously from 0x1fffffff to 0xe0000000. Therefore rewrite & fix emulation of the guest timer based on the monotonic kernel time (i.e. ktime_get()). Internally a 32-bit count_bias value is added to the frequency scaled nanosecond monotonic time to get the guest's CP0_Count. The frequency of the timer is initialised to 100MHz and cannot yet be changed, but a later patch will allow the frequency to be configured via the KVM_{GET,SET}_ONE_REG ioctl interface. The timer can now be stopped via the CP0_Cause.DC bit (by the guest or via the KVM_SET_ONE_REG ioctl interface), at which point the current CP0_Count is stored and can be read directly. When it is restarted the bias is recalculated such that the CP0_Count value is continuous. Due to the nature of hrtimer interrupts any read of the guest's CP0_Count register while it is running triggers a check for whether the hrtimer has expired, so that the guest/userland cannot observe the CP0_Count passing CP0_Compare without queuing a timer interrupt. This is also taken advantage of when stopping the timer to ensure that a pending timer interrupt is queued. This replaces the implementation of: - Guest read of CP0_Count - Guest write of CP0_Count - Guest write of CP0_Compare - Guest write of CP0_Cause - Guest read of HWR 2 (CC) with RDHWR - Host read of CP0_Count via KVM_GET_ONE_REG ioctl interface - Host write of CP0_Count via KVM_SET_ONE_REG ioctl interface - Host write of CP0_Compare via KVM_SET_ONE_REG ioctl interface - Host write of CP0_Cause via KVM_SET_ONE_REG ioctl interface Signed-off-by: James Hogan Cc: Paolo Bonzini Cc: Gleb Natapov Cc: kvm@vger.kernel.org Cc: Ralf Baechle Cc: linux-mips@linux-mips.org Cc: Sanjay Lal Signed-off-by: Paolo Bonzini --- diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h index 79410f85a5a7..75ed94aeefe7 100644 --- a/arch/mips/include/asm/kvm_host.h +++ b/arch/mips/include/asm/kvm_host.h @@ -404,8 +404,15 @@ struct kvm_vcpu_arch { u32 io_gpr; /* GPR used as IO source/target */ - /* Used to calibrate the virutal count register for the guest */ - int32_t host_cp0_count; + struct hrtimer comparecount_timer; + /* Count bias from the raw time */ + uint32_t count_bias; + /* Frequency of timer in Hz */ + uint32_t count_hz; + /* Dynamic nanosecond bias (multiple of count_period) to avoid overflow */ + s64 count_dyn_bias; + /* Period of timer tick in ns */ + u64 count_period; /* Bitmask of exceptions that are pending */ unsigned long pending_exceptions; @@ -426,8 +433,6 @@ struct kvm_vcpu_arch { uint32_t guest_kernel_asid[NR_CPUS]; struct mm_struct guest_kernel_mm, guest_user_mm; - struct hrtimer comparecount_timer; - int last_sched_cpu; /* WAIT executed */ @@ -705,7 +710,13 @@ extern enum emulation_result kvm_mips_emulate_bp_exc(unsigned long cause, extern enum emulation_result kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu, struct kvm_run *run); -enum emulation_result kvm_mips_emulate_count(struct kvm_vcpu *vcpu); +uint32_t kvm_mips_read_count(struct kvm_vcpu *vcpu); +void kvm_mips_write_count(struct kvm_vcpu *vcpu, uint32_t count); +void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare); +void kvm_mips_init_count(struct kvm_vcpu *vcpu); +void kvm_mips_count_enable_cause(struct kvm_vcpu *vcpu); +void kvm_mips_count_disable_cause(struct kvm_vcpu *vcpu); +enum hrtimer_restart kvm_mips_count_timeout(struct kvm_vcpu *vcpu); enum emulation_result kvm_mips_check_privilege(unsigned long cause, uint32_t *opc, Reading git-diff-tree failed