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Message-ID: <BYAPR21MB168844A39612131C920DA954D7399@BYAPR21MB1688.namprd21.prod.outlook.com>
Date: Wed, 2 Nov 2022 20:33:31 +0000
From: "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To: "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
KY Srinivasan <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
"wei.liu@...nel.org" <wei.liu@...nel.org>,
Dexuan Cui <decui@...rosoft.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...hat.com" <mingo@...hat.com>,
"bp@...en8.de" <bp@...en8.de>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
Arnd Bergmann <arnd@...db.de>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
CC: "stanislav.kinsburskiy@...il.com" <stanislav.kinsburskiy@...il.com>,
"kumarpraveen@...ux.microsoft.com" <kumarpraveen@...ux.microsoft.com>,
"mail@...rudhrb.com" <mail@...rudhrb.com>
Subject: RE: [PATCH v2 1/2] clocksource/drivers/hyperv: add data structure for
reference TSC MSR
From: Michael Kelley (LINUX) <mikelley@...rosoft.com> Sent: Thursday, October 27, 2022 6:43 AM
> From: Anirudh Rayabharam <anrayabh@...ux.microsoft.com> Sent: Thursday,
> October 27, 2022 2:57 AM
> >
> > Add a data structure to represent the reference TSC MSR similar to
> > other MSRs. This simplifies the code for updating the MSR.
> >
> > Signed-off-by: Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
> > ---
> > drivers/clocksource/hyperv_timer.c | 28 ++++++++++++++--------------
> > include/asm-generic/hyperv-tlfs.h | 9 +++++++++
> > 2 files changed, 23 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/clocksource/hyperv_timer.c
> b/drivers/clocksource/hyperv_timer.c
> > index bb47610bbd1c..11332c82d1af 100644
> > --- a/drivers/clocksource/hyperv_timer.c
> > +++ b/drivers/clocksource/hyperv_timer.c
> > @@ -395,25 +395,25 @@ static u64 notrace read_hv_sched_clock_tsc(void)
> >
> > static void suspend_hv_clock_tsc(struct clocksource *arg)
> > {
> > - u64 tsc_msr;
> > + union hv_reference_tsc_msr tsc_msr;
> >
> > /* Disable the TSC page */
> > - tsc_msr = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> > - tsc_msr &= ~BIT_ULL(0);
> > - hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
> > + tsc_msr.as_uint64 = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> > + tsc_msr.enable = 0;
> > + hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr.as_uint64);
> > }
> >
> >
> > static void resume_hv_clock_tsc(struct clocksource *arg)
> > {
> > phys_addr_t phys_addr = virt_to_phys(&tsc_pg);
> > - u64 tsc_msr;
> > + union hv_reference_tsc_msr tsc_msr;
> >
> > /* Re-enable the TSC page */
> > - tsc_msr = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> > - tsc_msr &= GENMASK_ULL(11, 0);
> > - tsc_msr |= BIT_ULL(0) | (u64)phys_addr;
> > - hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
> > + tsc_msr.as_uint64 = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> > + tsc_msr.enable = 1;
> > + tsc_msr.pfn = __phys_to_pfn(phys_addr);
My previous review missed a problem here (and in the similar line below).
__phys_to_pfn() will return a PFN based on the guest page size, which might
be different from Hyper-V's page size that is always 4K. This needs to be a
Hyper-V PFN, and we have virt_to_hvpfn() available to do just that, assuming
that function is safe to use here and in the case below.
Michael
> > + hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr.as_uint64);
> > }
> >
> > #ifdef HAVE_VDSO_CLOCKMODE_HVCLOCK
> > @@ -495,7 +495,7 @@ static __always_inline void hv_setup_sched_clock(void
> > *sched_clock) {}
> >
> > static bool __init hv_init_tsc_clocksource(void)
> > {
> > - u64 tsc_msr;
> > + union hv_reference_tsc_msr tsc_msr;
> > phys_addr_t phys_addr;
> >
> > if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
> > @@ -530,10 +530,10 @@ static bool __init hv_init_tsc_clocksource(void)
> > * (which already has at least the low 12 bits set to zero since
> > * it is page aligned). Also set the "enable" bit, which is bit 0.
> > */
> > - tsc_msr = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> > - tsc_msr &= GENMASK_ULL(11, 0);
> > - tsc_msr = tsc_msr | 0x1 | (u64)phys_addr;
> > - hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
> > + tsc_msr.as_uint64 = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> > + tsc_msr.enable = 1;
> > + tsc_msr.pfn = __phys_to_pfn(phys_addr);
> > + hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr.as_uint64);
> >
> > clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
> >
> > diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> > index fdce7a4cfc6f..b17c6eeb9afa 100644
> > --- a/include/asm-generic/hyperv-tlfs.h
> > +++ b/include/asm-generic/hyperv-tlfs.h
> > @@ -102,6 +102,15 @@ struct ms_hyperv_tsc_page {
> > volatile s64 tsc_offset;
> > } __packed;
> >
> > +union hv_reference_tsc_msr {
> > + u64 as_uint64;
> > + struct {
> > + u64 enable:1;
> > + u64 reserved:11;
> > + u64 pfn:52;
> > + } __packed;
> > +};
> > +
> > /*
> > * The guest OS needs to register the guest ID with the hypervisor.
> > * The guest ID is a 64 bit entity and the structure of this ID is
> > --
> > 2.34.1
>
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
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