> -----Original Message-----
> From: Wei Liu <[email protected]> On Behalf Of Wei Liu
> Sent: 18 December 2019 14:43
> To: Xen Development List <[email protected]>
> Cc: Michael Kelley <[email protected]>; Durrant, Paul
> <[email protected]>; Wei Liu <[email protected]>; Jan Beulich
> <[email protected]>; Andrew Cooper <[email protected]>; Wei Liu
> <[email protected]>; Roger Pau Monné <[email protected]>
> Subject: [PATCH v2 6/6] x86: implement Hyper-V clock source
>
> Implement a clock source using Hyper-V's reference TSC page.
>
> Signed-off-by: Wei Liu <[email protected]>
> ---
> v2:
> 1. Address Jan's comments.
>
> Relevant spec:
>
> https://github.com/MicrosoftDocs/Virtualization-
> Documentation/raw/live/tlfs/Hypervisor%20Top%20Level%20Functional%20Specif
> ication%20v5.0C.pdf
>
> Section 12.6.
> ---
> xen/arch/x86/time.c | 101 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 101 insertions(+)
>
> diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> index 216169a025..8b96b2e9a5 100644
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -31,6 +31,7 @@
> #include <asm/processor.h>
> #include <asm/fixmap.h>
> #include <asm/guest.h>
> +#include <asm/guest/hyperv-tlfs.h>
> #include <asm/mc146818rtc.h>
> #include <asm/div64.h>
> #include <asm/acpi.h>
> @@ -644,6 +645,103 @@ static struct platform_timesource __initdata
> plt_xen_timer =
> };
> #endif
>
> +#ifdef CONFIG_HYPERV_GUEST
> +/************************************************************
> + * HYPER-V REFERENCE TSC
> + */
> +
> +static struct ms_hyperv_tsc_page *hyperv_tsc;
> +static struct page_info *hyperv_tsc_page;
> +
> +static int64_t __init init_hyperv_timer(struct platform_timesource *pts)
> +{
> + paddr_t maddr;
> + uint64_t tsc_msr, freq;
> +
> + if ( !(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE) )
> + return 0;
> +
> + hyperv_tsc_page = alloc_domheap_page(NULL, 0);
> + if ( !hyperv_tsc_page )
> + return 0;
> +
> + hyperv_tsc = __map_domain_page_global(hyperv_tsc_page);
> + if ( !hyperv_tsc )
> + {
> + free_domheap_page(hyperv_tsc_page);
> + hyperv_tsc_page = NULL;
> + return 0;
> + }
> +
> + maddr = page_to_maddr(hyperv_tsc_page);
> +
> + /*
> + * Per Hyper-V TLFS:
> + * 1. Read existing MSR value
> + * 2. Preserve bits [11:1]
> + * 3. Set bits [63:12] to be guest physical address of tsc page
> + * 4. Set enabled bit (0)
> + * 5. Write back new MSR value
> + */
> + rdmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr);
> + tsc_msr &= 0xffeULL;
> + tsc_msr |= maddr | 1 /* enabled */;
> + wrmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr);
> +
You need to check for the HV_X64_ACCESS_FREQUENCY_MSRS feature or you risk a
#GP below I think.
> + /* Get TSC frequency from Hyper-V */
> + rdmsrl(HV_X64_MSR_TSC_FREQUENCY, freq);
> + pts->frequency = freq;
> +
> + return freq;
> +}
> +
> +static inline uint64_t read_hyperv_timer(void)
> +{
> + uint64_t scale, offset, ret, tsc;
> + uint32_t seq;
> + const struct ms_hyperv_tsc_page *tsc_page = hyperv_tsc;
> +
> + do {
> + seq = tsc_page->tsc_sequence;
> +
> + /* Seq 0 is special. It means the TSC enlightenment is not
> + * available at the moment. The reference time can only be
> + * obtained from the Reference Counter MSR.
> + */
> + if ( seq == 0 )
Older versions of the spec used to use 0xFFFFFFFF I think, although when I look
again they seem to have been retro-actively fixed. In any case I think you
should treat both 0xFFFFFFFF and 0 as invalid.
> + {
> + rdmsrl(HV_X64_MSR_TIME_REF_COUNT, ret);
> + return ret;
> + }
> +
> + /* rdtsc_ordered already contains a load fence */
> + tsc = rdtsc_ordered();
> + scale = tsc_page->tsc_scale;
> + offset = tsc_page->tsc_offset;
> +
> + smp_rmb();
> +
> + } while (tsc_page->tsc_sequence != seq);
> +
> + /* ret = ((tsc * scale) >> 64) + offset; */
> + asm ( "mul %[scale]; add %[offset], %[ret]"
> + : "+a" (tsc), [ret] "=d" (ret)
> + : [scale] "rm" (scale), [offset] "rm" (offset) );
> +
It would be nice to common this up with scale_tsc() in viridian/time.c.
Paul
> + return ret;
> +}
> +
> +static struct platform_timesource __initdata plt_hyperv_timer =
> +{
> + .id = "hyperv",
> + .name = "HYPER-V REFERENCE TSC",
> + .read_counter = read_hyperv_timer,
> + .init = init_hyperv_timer,
> + /* See TSC time source for why counter_bits is set to 63 */
> + .counter_bits = 63,
> +};
> +#endif
> +
> /************************************************************
> * GENERIC PLATFORM TIMER INFRASTRUCTURE
> */
> @@ -793,6 +891,9 @@ static u64 __init init_platform_timer(void)
> static struct platform_timesource * __initdata plt_timers[] = {
> #ifdef CONFIG_XEN_GUEST
> &plt_xen_timer,
> +#endif
> +#ifdef CONFIG_HYPERV_GUEST
> + &plt_hyperv_timer,
> #endif
> &plt_hpet, &plt_pmtimer, &plt_pit
> };
> --
> 2.20.1
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