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    SubjectRe: Direct rdtsc call side-effect
    On Thu, Jun 01, 2023 at 10:56:03AM +0200, Peter Zijlstra wrote:
    > On Thu, Jun 01, 2023 at 01:45:35PM +0500, Muhammad Usama Anjum wrote:
    > > Hi,
    > >
    > > I've been looking into a problem where Windows applications misbehave
    > > across suspend/resume when run on Wine on x86. These applications see time
    > > going backwards. The timestamp counter (TSC) is reset when system resumes.
    > > In case of Windows on Intel and AMD, the timestamp is saved and restored
    > > when the system resumes from suspend.
    > >
    > > These applications read timestamp by rdtsc directly. These calls cannot be
    > > intercepted by Wine. The application should be fixed such that it handles
    > > these scenarios correctly. But there are hundreds of applications which
    > > cannot be fixed. So some support is required in Wine or kernel. There isn't
    > > anything which Wine can do as rdtsc call directly reads the timestamp. The
    > > only option is that we support something in kernel.
    > >
    > > As more and more things are being added to Wine, Windows application can be
    > > run pretty easily on Linux. But this rdtsc is a big hurdle. What are your
    > > thoughts on solving this problem?
    > >
    > > We are thinking of saving and restoring the timestamp counter at suspend
    > > and resume time respectively. In theory it can work on Intel because of
    > > TSC_ADJUST register. But it'll never work on AMD until:
    > > * AMD supports the same kind of adjust register. (AMD has said that the
    > > adjust register cannot be implemented in their firmware. They'll have to
    > > add it to their hardware.)
    > > * by manual synchronization in kernel (I know you don't like this idea. But
    > > there is something Windows is doing to save/restore and sync the TSC)
    >
    > Wine could set TIF_NOTSC, which will cause it to run with CR4.TSD
    > cleared and cause RDTSC to #GP, at which point you can emulate it.

    The other option is to have Wine run itself in a (KVM) virtual machine
    and mess with the VMM TSC offset :-)

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