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Re: [Xen-devel] [PATCH V4 2/4] x86/altp2m: Add hypercall to set a range of sve bits
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>
- Date: Wed, 18 Dec 2019 08:45:10 +0000
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- Thread-topic: [Xen-devel] [PATCH V4 2/4] x86/altp2m: Add hypercall to set a range of sve bits
On 18.12.2019 10:13, Alexandru Stefan ISAILA wrote:
>
>>> +/*
>>> + * Set/clear the #VE suppress bit for multiple pages. Only available on
>>> VMX.
>>> + */
>>> +int p2m_set_suppress_ve_multi(struct domain *d,
>>> + struct xen_hvm_altp2m_suppress_ve_multi *sve)
>>> +{
>>> + struct p2m_domain *host_p2m = p2m_get_hostp2m(d);
>>> + struct p2m_domain *ap2m = NULL;
>>> + struct p2m_domain *p2m = host_p2m;
>>> + uint64_t start = sve->first_gfn;
>>> + int rc = 0;
>>> + uint64_t max_phys_addr = (1UL << d->arch.cpuid->extd.maxphysaddr) - 1;
>>> +
>>> + if ( sve->view > 0 )
>>> + {
>>> + if ( sve->view >= MAX_ALTP2M ||
>>> + d->arch.altp2m_eptp[array_index_nospec(sve->view, MAX_EPTP)]
>>> ==
>>> + mfn_x(INVALID_MFN) )
>>> + return -EINVAL;
>>> +
>>> + p2m = ap2m = d->arch.altp2m_p2m[array_index_nospec(sve->view,
>>> + MAX_ALTP2M)];
>>> + }
>>> +
>>> + p2m_lock(host_p2m);
>>> +
>>> + if ( ap2m )
>>> + p2m_lock(ap2m);
>>> +
>>> + while ( sve->last_gfn >= start && start < max_phys_addr )
>>
>> Why don't you clip ->last_gfn ahead of the loop, saving one
>> comparison per iteration?
>
> I've done this so it will have fewer lines but sure, I can have the
> ->last_gfn check before the loop.
>
Wouldn't there be a issue if start goes over ->last_gfn and there is no
break for preemption? Then the loop will run until max_phys_addr.
Alex
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