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[hyperv] Provide timer based on the 10MHz time reference count MSR
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When running on AMD platforms, the legacy hardware emulation is
extremely unreliable.  In particular, the IRQ0 timer interrupt is
likely to simply stop working, resulting in a total failure of any
code that relies on timers (such as DHCP retransmission attempts).

Work around this by using the 10MHz time counter provided by Hyper-V
via an MSR.  (This timer can be tested in KVM via the command-line
option "-cpu host,hv_time".)

Signed-off-by: Michael Brown <mcb30@ipxe.org>
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@mcb30
mcb30 committed Jan 26, 2017
1 parent 302f1ee commit f3ba0fb
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Showing 2 changed files with 108 additions and 11 deletions.
113 changes: 102 additions & 11 deletions src/arch/x86/drivers/hyperv/hyperv.c
View file
Expand Up @@ -39,6 +39,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <pic8259.h>
#include <ipxe/malloc.h>
#include <ipxe/device.h>
#include <ipxe/timer.h>
#include <ipxe/cpuid.h>
#include <ipxe/msr.h>
#include <ipxe/hyperv.h>
Expand All @@ -51,6 +52,12 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
*/
#define HV_MESSAGE_MAX_WAIT_MS 1000

/** Hyper-V timer frequency (fixed 10Mhz) */
#define HV_TIMER_HZ 10000000

/** Hyper-V timer scale factor (used to avoid 64-bit division) */
#define HV_TIMER_SHIFT 18

/**
* Convert a Hyper-V status code to an iPXE status code
*
Expand Down Expand Up @@ -145,34 +152,46 @@ static void hv_free_message ( struct hv_hypervisor *hv ) {
/**
* Check whether or not we are running in Hyper-V
*
* @v hv Hyper-V hypervisor
* @ret rc Return status code
*/
static int hv_check_hv ( struct hv_hypervisor *hv ) {
static int hv_check_hv ( void ) {
struct x86_features features;
uint32_t interface_id;
uint32_t discard_ebx;
uint32_t discard_ecx;
uint32_t discard_edx;
uint32_t available;
uint32_t permissions;

/* Check for presence of a hypervisor (not necessarily Hyper-V) */
x86_features ( &features );
if ( ! ( features.intel.ecx & CPUID_FEATURES_INTEL_ECX_HYPERVISOR ) ) {
DBGC ( hv, "HV %p not running in a hypervisor\n", hv );
DBGC ( HV_INTERFACE_ID, "HV not running in a hypervisor\n" );
return -ENODEV;
}

/* Check that hypervisor is Hyper-V */
cpuid ( HV_CPUID_INTERFACE_ID, &interface_id, &discard_ebx,
&discard_ecx, &discard_edx );
if ( interface_id != HV_INTERFACE_ID ) {
DBGC ( hv, "HV %p not running in Hyper-V (interface ID "
"%#08x)\n", hv, interface_id );
DBGC ( HV_INTERFACE_ID, "HV not running in Hyper-V (interface "
"ID %#08x)\n", interface_id );
return -ENODEV;
}

return 0;
}

/**
* Check required features
*
* @v hv Hyper-V hypervisor
* @ret rc Return status code
*/
static int hv_check_features ( struct hv_hypervisor *hv ) {
uint32_t available;
uint32_t permissions;
uint32_t discard_ecx;
uint32_t discard_edx;

/* Check that required features and privileges are available */
cpuid ( HV_CPUID_FEATURES, &available, &permissions, &discard_ecx,
&discard_edx );
Expand Down Expand Up @@ -509,16 +528,20 @@ static int hv_probe ( struct root_device *rootdev ) {
struct hv_hypervisor *hv;
int rc;

/* Check we are running in Hyper-V */
if ( ( rc = hv_check_hv() ) != 0 )
goto err_check_hv;

/* Allocate and initialise structure */
hv = zalloc ( sizeof ( *hv ) );
if ( ! hv ) {
rc = -ENOMEM;
goto err_alloc;
}

/* Check we are running in Hyper-V */
if ( ( rc = hv_check_hv ( hv ) ) != 0 )
goto err_check_hv;
/* Check features */
if ( ( rc = hv_check_features ( hv ) ) != 0 )
goto err_check_features;

/* Allocate pages */
if ( ( rc = hv_alloc_pages ( hv, &hv->hypercall, &hv->synic.message,
Expand Down Expand Up @@ -555,9 +578,10 @@ static int hv_probe ( struct root_device *rootdev ) {
hv_free_pages ( hv, hv->hypercall, hv->synic.message, hv->synic.event,
NULL );
err_alloc_pages:
err_check_hv:
err_check_features:
free ( hv );
err_alloc:
err_check_hv:
return rc;
}

Expand Down Expand Up @@ -590,6 +614,73 @@ struct root_device hv_root_device __root_device = {
.driver = &hv_root_driver,
};

/**
* Probe timer
*
* @ret rc Return status code
*/
static int hv_timer_probe ( void ) {
uint32_t available;
uint32_t discard_ebx;
uint32_t discard_ecx;
uint32_t discard_edx;
int rc;

/* Check we are running in Hyper-V */
if ( ( rc = hv_check_hv() ) != 0 )
return rc;

/* Check for available reference counter */
cpuid ( HV_CPUID_FEATURES, &available, &discard_ebx, &discard_ecx,
&discard_edx );
if ( ! ( available & HV_FEATURES_AVAIL_TIME_REF_COUNT_MSR ) ) {
DBGC ( HV_INTERFACE_ID, "HV has no time reference counter\n" );
return -ENODEV;
}

return 0;
}

/**
* Get current system time in ticks
*
* @ret ticks Current time, in ticks
*/
static unsigned long hv_currticks ( void ) {

/* Calculate time using a combination of bit shifts and
* multiplication (to avoid a 64-bit division).
*/
return ( ( rdmsr ( HV_X64_MSR_TIME_REF_COUNT ) >> HV_TIMER_SHIFT ) *
( TICKS_PER_SEC / ( HV_TIMER_HZ >> HV_TIMER_SHIFT ) ) );
}

/**
* Delay for a fixed number of microseconds
*
* @v usecs Number of microseconds for which to delay
*/
static void hv_udelay ( unsigned long usecs ) {
uint32_t start;
uint32_t elapsed;
uint32_t threshold;

/* Spin until specified number of 10MHz ticks have elapsed */
start = rdmsr ( HV_X64_MSR_TIME_REF_COUNT );
threshold = ( usecs * ( HV_TIMER_HZ / 1000000 ) );
do {
elapsed = ( rdmsr ( HV_X64_MSR_TIME_REF_COUNT ) - start );
} while ( elapsed < threshold );
}

/** Hyper-V timer */
struct timer hv_timer __timer ( TIMER_PREFERRED ) = {
.name = "Hyper-V",
.probe = hv_timer_probe,
.currticks = hv_currticks,
.udelay = hv_udelay,
};

/* Drag in objects via hv_root_device */
REQUIRING_SYMBOL ( hv_root_device );

Expand Down
6 changes: 6 additions & 0 deletions src/arch/x86/drivers/hyperv/hyperv.h
View file
Expand Up @@ -21,6 +21,9 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/** Get hypervisor features */
#define HV_CPUID_FEATURES 0x40000003UL

/** Time reference counter MSR is available */
#define HV_FEATURES_AVAIL_TIME_REF_COUNT_MSR 0x00000002UL

/** SynIC MSRs are available */
#define HV_FEATURES_AVAIL_SYNIC_MSR 0x00000004UL

Expand All @@ -39,6 +42,9 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/** Hypercall page MSR */
#define HV_X64_MSR_HYPERCALL 0x40000001UL

/** Time reference MSR */
#define HV_X64_MSR_TIME_REF_COUNT 0x40000020UL

/** SynIC control MSR */
#define HV_X64_MSR_SCONTROL 0x40000080UL

Expand Down

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