> -----Original Message----- > From: Sean Christopherson <seanjc@xxxxxxxxxx> > Sent: Saturday, February 4, 2023 4:50 AM > To: Li,Rongqing <lirongqing@xxxxxxxxx> > Cc: kvm@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx > Subject: Re: [PATCH] KVM: x86: Enable PIT shutdown quirk > > Please use "x86/kvm:" for guest side changes. > > On Fri, Feb 03, 2023, lirongqing@xxxxxxxxx wrote: > > From: Li RongQing <lirongqing@xxxxxxxxx> > > > > KVM emulation of the PIT has a quirk such that the normal PIT shutdown > > path doesn't work, because clearing the counter register restarts the > > timer. > > > > Disable the counter clearing on PIT shutdown as in Hyper-V > > > > Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx> > > --- > > arch/x86/kernel/kvm.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index > > 1cceac5..14411b6 100644 > > --- a/arch/x86/kernel/kvm.c > > +++ b/arch/x86/kernel/kvm.c > > @@ -43,6 +43,7 @@ > > #include <asm/reboot.h> > > #include <asm/svm.h> > > #include <asm/e820/api.h> > > +#include <linux/i8253.h> > > > > DEFINE_STATIC_KEY_FALSE(kvm_async_pf_enabled); > > > > @@ -978,6 +979,9 @@ static void __init kvm_init_platform(void) > > wrmsrl(MSR_KVM_MIGRATION_CONTROL, > > KVM_MIGRATION_READY); > > } > > + > > + i8253_clear_counter_on_shutdown = false; > > AFAICT, zeroing the counter isn't actually supposed to stop it from counting. > Copy pasting from the KVM host-side patch[*]: > > The largest possible initial count is 0; this is equivalent to 216 for > binary counting and 104 for BCD counting. > > The Counter does not stop when it reaches zero. In Modes 0, 1, 4, and 5 the > Counter ‘‘wraps around’’ to the highest count, either FFFF hex for binary > count- > ing or 9999 for BCD counting, and continues counting. > > Mode 0 is typically used for event counting. After the Control Word is written, > OUT is initially low, and will remain low until the Counter reaches zero. OUT > then goes high and remains high until a new count or a new Mode 0 Control > Word > is written into the Counter. > > Can we simply delete i8253_clear_counter_on_shutdown and the code it > wraps? > The git log did not record why counter register should be zeroed I will try to delete the zeroing counter register codes Thanks -Li > [*] https://lore.kernel.org/kvm/Y91yLt3EZLA32csp@xxxxxxxxxx
