On Mon, 2024-04-22 at 14:22 +0200, Paolo Bonzini wrote:
On Thu, Apr 18, 2024 at 9:51 PM David Woodhouse dwmw2@infradead.org wrote:
gpa_t time; struct pvclock_vcpu_time_info hv_clock; - unsigned int hw_tsc_khz; + unsigned int hw_tsc_hz;
Why not change this to u64? 4.3 GHz is scarily close to current processors, though I expect that it will break a lot more software than just KVM.
I'm not sure that just changing the variable is sufficient. I'm concerned that we may still have places (like kvm_get_time_scale(), although it's hard to tell because it's entirely uncommented!) which assume that they can multiply the value by *any* 32-bit number and it'll still fit in 64 bits.
static int kvm_guest_time_update(struct kvm_vcpu *v) { - unsigned long flags, tgt_tsc_khz; + unsigned long flags; + uint64_t tgt_tsc_hz;
... especially considering that you did use a 64-bit integer here (though---please use u64 not uint64_t; and BTW if you want to add a patch to change kvm_get_time_scale() to u64, please do.
Meh, I'm used to programming in C. Yes, I *am* old enough to have been doing this since the last decade of the 1900s, but it *has* been a long time since 1999, and my fingers have learned :)
That said, although I *do* write in C by default, where I'm editing functions which already have that old anachronistic crap, I generally manage to go back and change my additions from proper C to match their surroundings. And I suppose there *are* some of those awful u64/s64 types already in kvm_guest_time_update(), so I would normally have done so. I'll change that in my tree.
No way I'm regressing kvm_get_time_scale() myself though :)
Heh, looks like it was you who made it uint64_t, in 2016. In a commit (3ae13faac) which said "Prepare for improving the precision in the next patch"... which never came, AFAICT?