From: Paul Durrant Date: Thu, 23 Mar 2017 14:51:45 +0000 (+0100) Subject: x86/viridian: make the threshold for HvNotifyLongSpinWait tunable X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~2418 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=bf13fe76c5bc8d4a9570aa0a8eb168cfe7fbe8d5;p=xen.git x86/viridian: make the threshold for HvNotifyLongSpinWait tunable The current threshold before the guest issues the hypercall is, and always has been, hard-coded to 2047. It is not clear where this number came from so, to at least allow for ease of experimentation, this patch makes the threshold tunable via the Xen command line. Signed-off-by: Paul Durrant Reviewed-by: Jan Beulich --- diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown index c81d6936b2..bdbdb8a53b 100644 --- a/docs/misc/xen-command-line.markdown +++ b/docs/misc/xen-command-line.markdown @@ -1624,6 +1624,14 @@ relinquish control to dom0. , and must be integers. The values will be encoded in guest CPUID 0x40000002 if viridian enlightenments are enabled. +### viridian-spinlock-retry-count +> `= ` + +> Default: `2047` + +Specify the maximum number of retries before an enlightened Windows +guest will notify Xen that it has failed to acquire a spinlock. + ### vpid (Intel) > `= ` diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c index d59294fb18..4c65ddca54 100644 --- a/xen/arch/x86/hvm/viridian.c +++ b/xen/arch/x86/hvm/viridian.c @@ -174,6 +174,14 @@ static uint16_t __read_mostly viridian_major = 6; static uint16_t __read_mostly viridian_minor = 0; static uint32_t __read_mostly viridian_build = 0x1772; +/* + * Maximum number of retries before the guest will notify of failure + * to acquire a spinlock. + */ +static uint32_t __read_mostly viridian_spinlock_retry_count = 2047; +integer_param("viridian-spinlock-retry-count", + viridian_spinlock_retry_count); + void cpuid_viridian_leaves(const struct vcpu *v, uint32_t leaf, uint32_t subleaf, struct cpuid_leaf *res) { @@ -251,7 +259,13 @@ void cpuid_viridian_leaves(const struct vcpu *v, uint32_t leaf, res->a |= CPUID4A_HCALL_REMOTE_TLB_FLUSH; if ( !cpu_has_vmx_apic_reg_virt ) res->a |= CPUID4A_MSR_BASED_APIC; - res->b = 2047; /* long spin count */ + + /* + * This value is the recommended number of attempts to try to + * acquire a spinlock before notifying the hypervisor via the + * HvNotifyLongSpinWait hypercall. + */ + res->b = viridian_spinlock_retry_count; break; case 6: