This patch does not need to be backported to any stable releases. It is prep work for guests on Hyper-V ARM64 when the guest page size is 16K or 64K, and that functionality isn't upstream yet. Michael > -----Original Message----- > From: Sasha Levin <sashal@xxxxxxxxxx> > Sent: Friday, February 14, 2020 7:46 AM > To: linux-kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx > Cc: Boqun Feng <boqun.feng@xxxxxxxxx>; linux-hyperv@xxxxxxxxxxxxxxx; Michael Kelley > <mikelley@xxxxxxxxxxxxx>; Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>; Sasha Levin > <sashal@xxxxxxxxxx> > Subject: [PATCH AUTOSEL 5.5 389/542] clocksource/drivers/hyper-v: Reserve PAGE_SIZE > space for tsc page > > From: Boqun Feng <boqun.feng@xxxxxxxxx> > > [ Upstream commit ddc61bbc45017726a2b450350d476b4dc5ae25ce ] > > Currently, the reserved size for a tsc page is 4K, which is enough for > communicating with hypervisor. However, in the case where we want to > export the tsc page to userspace (e.g. for vDSO to read the > clocksource), the tsc page should be at least PAGE_SIZE, otherwise, when > PAGE_SIZE is larger than 4K, extra kernel data will be mapped into > userspace, which means leaking kernel information. > > Therefore reserve PAGE_SIZE space for tsc_pg as a preparation for the > vDSO support of ARM64 in the future. Also, while at it, replace all > reference to tsc_pg with hv_get_tsc_page() since it should be the only > interface to access tsc page. > > Signed-off-by: Boqun Feng (Microsoft) <boqun.feng@xxxxxxxxx> > Cc: linux-hyperv@xxxxxxxxxxxxxxx > Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx> > Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> > Link: > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fr > %2F20191126021723.4710-1- > boqun.feng%40gmail.com&data=02%7C01%7Cmikelley%40microsoft.com%7C2f481a9 > 3db624cb4b5e208d7b16691f6%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C6371 > 72926408924092&sdata=%2F1JNMBiq7l1ufSsWphZb%2FMLNep2EIOCzlXcG%2F9foZNw > %3D&reserved=0 > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> > --- > drivers/clocksource/hyperv_timer.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c > index 287d8d58c21ac..b6ea3a2093c56 100644 > --- a/drivers/clocksource/hyperv_timer.c > +++ b/drivers/clocksource/hyperv_timer.c > @@ -307,17 +307,20 @@ EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup); > struct clocksource *hyperv_cs; > EXPORT_SYMBOL_GPL(hyperv_cs); > > -static struct ms_hyperv_tsc_page tsc_pg __aligned(PAGE_SIZE); > +static union { > + struct ms_hyperv_tsc_page page; > + u8 reserved[PAGE_SIZE]; > +} tsc_pg __aligned(PAGE_SIZE); > > struct ms_hyperv_tsc_page *hv_get_tsc_page(void) > { > - return &tsc_pg; > + return &tsc_pg.page; > } > EXPORT_SYMBOL_GPL(hv_get_tsc_page); > > static u64 notrace read_hv_clock_tsc(struct clocksource *arg) > { > - u64 current_tick = hv_read_tsc_page(&tsc_pg); > + u64 current_tick = hv_read_tsc_page(hv_get_tsc_page()); > > if (current_tick == U64_MAX) > hv_get_time_ref_count(current_tick); > @@ -372,7 +375,7 @@ static bool __init hv_init_tsc_clocksource(void) > return false; > > hyperv_cs = &hyperv_cs_tsc; > - phys_addr = virt_to_phys(&tsc_pg); > + phys_addr = virt_to_phys(hv_get_tsc_page()); > > /* > * The Hyper-V TLFS specifies to preserve the value of reserved > -- > 2.20.1
