From: Stanislav Kinsburskiy <stanislav.kinsburskiy@xxxxxxxxx> Sent: Wednesday, November 2, 2022 12:26 PM > ср, 2 нояб. 2022 г. в 12:07, Michael Kelley (LINUX) <mailto:mikelley@xxxxxxxxxxxxx>: > From: Stanislav Kinsburskii <mailto:skinsburskii@xxxxxxxxxxxxxxxxxxx> Sent: Tuesday, November 1, 2022 10:31 AM > > > > And rework the code to use it instead of the physical address. > > This is a cleanup and precursor patch for upcoming support for TSC page > > mapping into hyper-v root partition. > > > > drivers/clocksource/hyperv_timer.c | 14 +++++++++----- > > 1 file changed, 9 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c > > index c4dbf40a3d3e..d447bc99a399 100644 > > --- a/drivers/clocksource/hyperv_timer.c > > +++ b/drivers/clocksource/hyperv_timer.c > > @@ -367,6 +367,12 @@ static union { > > } tsc_pg __aligned(PAGE_SIZE); > > > > static struct ms_hyperv_tsc_page *tsc_page = &tsc_pg.page; > > +static unsigned long tsc_pfn; > > + > > +static unsigned long hv_get_tsc_pfn(void) > > +{ > > + return tsc_pfn; > > +} > > > It makes sense to have the tsc_page global variable so that we can > > handle the root partition and guest partition cases with common code, > > even though the TSC page memory originates differently in the two cases. > > > > But do we also need a tsc_pfn global variable and getter function? When > > the PFN is needed, conversion from the tsc_page virtual address to the PFN > > isn't hard, and such a conversion is needed in only a couple of places. To me, > > it's simpler to keep a single global variable and getter function (i.e., > > hv_get_tsc_page), and do the conversions where needed. Adding tsc_pfn > > and the getter function introduces a fair amount of code churn for not much > > benefit. It's a judgment call, but that's my $.02. > > As I replied to Anirudh , AFAIK virt_to_phys doesn't work for remapped pages. > Another option would be to read the MSR each time PFN has to be returned to > the vvar mapping function (i.e. on every fork), which introduces unnecessary > performance regression.. > Another modification would be to make pfn a static variable and initialize it > once in hv_get_tsc_pfn() on first access. But I like this implementation less. Valid point about virt_to_phys(). But virt_to_hvpfn() does the right thing. It distinguishes between kernel addresses in the main linear mapping and vmalloc() addresses, which is what you get from memremap(). But I haven't looked through all the places virt_to_hvpfn() would be needed to make sure it's safe to use. However, thinking about virt_to_hvpfn(), there's a problem with Anirudh's earlier patch set that started using __phys_to_pfn(). That won't work correctly if the guest page size is not 4K because it will return a PFN based on the guest page size, not based on Hyper-V's expectation that the PFN is based on a 4K page size. So that needs to be fixed either way. Michael
