From c5e8ec8e9beffb9481dba27ab5048c03c8585d7d Mon Sep 17 00:00:00 2001 From: Denis Plotnikov Date: Fri, 7 Apr 2017 12:09:52 +0300 Subject: [PATCH] KVM: x86: remaster kvm_write_tsc code MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Reuse existing code instead of using inline asm. Make the code more concise and clear in the TSC synchronization part. Signed-off-by: Denis Plotnikov Reviewed-by: Roman Kagan Signed-off-by: Radim Krčmář --- arch/x86/kvm/x86.c | 52 ++++++++++++---------------------------------- 1 file changed, 13 insertions(+), 39 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3046b7f278ae..422f803fa365 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1443,10 +1443,10 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr) struct kvm *kvm = vcpu->kvm; u64 offset, ns, elapsed; unsigned long flags; - s64 usdiff; bool matched; bool already_matched; u64 data = msr->data; + bool synchronizing = false; raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags); offset = kvm_compute_tsc_offset(vcpu, data); @@ -1454,51 +1454,25 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr) elapsed = ns - kvm->arch.last_tsc_nsec; if (vcpu->arch.virtual_tsc_khz) { - int faulted = 0; - - /* n.b - signed multiplication and division required */ - usdiff = data - kvm->arch.last_tsc_write; -#ifdef CONFIG_X86_64 - usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz; -#else - /* do_div() only does unsigned */ - asm("1: idivl %[divisor]\n" - "2: xor %%edx, %%edx\n" - " movl $0, %[faulted]\n" - "3:\n" - ".section .fixup,\"ax\"\n" - "4: movl $1, %[faulted]\n" - " jmp 3b\n" - ".previous\n" - - _ASM_EXTABLE(1b, 4b) - - : "=A"(usdiff), [faulted] "=r" (faulted) - : "A"(usdiff * 1000), [divisor] "rm"(vcpu->arch.virtual_tsc_khz)); - -#endif - do_div(elapsed, 1000); - usdiff -= elapsed; - if (usdiff < 0) - usdiff = -usdiff; - - /* idivl overflow => difference is larger than USEC_PER_SEC */ - if (faulted) - usdiff = USEC_PER_SEC; - } else - usdiff = USEC_PER_SEC; /* disable TSC match window below */ + u64 tsc_exp = kvm->arch.last_tsc_write + + nsec_to_cycles(vcpu, elapsed); + u64 tsc_hz = vcpu->arch.virtual_tsc_khz * 1000LL; + /* + * Special case: TSC write with a small delta (1 second) + * of virtual cycle time against real time is + * interpreted as an attempt to synchronize the CPU. + */ + synchronizing = data < tsc_exp + tsc_hz && + data + tsc_hz > tsc_exp; + } /* - * Special case: TSC write with a small delta (1 second) of virtual - * cycle time against real time is interpreted as an attempt to - * synchronize the CPU. - * * For a reliable TSC, we can match TSC offsets, and for an unstable * TSC, we add elapsed time in this computation. We could let the * compensation code attempt to catch up if we fall behind, but * it's better to try to match offsets from the beginning. */ - if (usdiff < USEC_PER_SEC && + if (synchronizing && vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) { if (!check_tsc_unstable()) { offset = kvm->arch.cur_tsc_offset; -- 2.20.1