Re: [PATCH v5 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active

[Brijesh Singh]

On 09/06/2018 09:07 AM, Sean Christopherson wrote:
...

> > +
> > +/* This should cover upto 512 VCPUS (first 64 are covered by hv_clock_boot[]). */
> > +#define HVC_DECRYPTED_ARRAY_SIZE \
> > +	((PAGE_SIZE * 7)  / sizeof(struct pvclock_vsyscall_time_info))
>
> I think we can define the size relative to NR_CPUS rather than picking
> an arbitrary number of pages, maybe with a BUILD_BUG_ON to make sure
> the total size won't require a second 2mb page for __decrpyted.
>
> #define HVC_DECRYPTED_ARRAY_SIZE  \
> 	PAGE_ALIGN((NR_CPUS - HVC_BOOT_ARRAY_SIZE) * \
> 		   sizeof(struct pvclock_vsyscall_time_info))

Sure works for me.

> > +static struct pvclock_vsyscall_time_info
> > +			hv_clock_dec[HVC_DECRYPTED_ARRAY_SIZE] __decrypted_hvclock;
> > +
> >   static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void)
> >   {
> >   	return &this_cpu_read(hv_clock_per_cpu)->pvti;
> > @@ -267,10 +274,19 @@ static int kvmclock_setup_percpu(unsigned int cpu)
> >   		return 0;
> >   
> >   	/* Use the static page for the first CPUs, allocate otherwise */
> > -	if (cpu < HVC_BOOT_ARRAY_SIZE)
> > +	if (cpu < HVC_BOOT_ARRAY_SIZE) {
> >   		p = &hv_clock_boot[cpu];
> > -	else
> > -		p = kzalloc(sizeof(*p), GFP_KERNEL);
> > +	} else {
> > +		/*
> > +		 * When SEV is active, use the static pages from
> > +		 * .data..decrypted_hvclock section. The pages are already
> > +		 * mapped with C=0.
> > +		 */
> > +		if (sev_active())
> > +			p = &hv_clock_dec[cpu - HVC_BOOT_ARRAY_SIZE];
> > +		else
> > +			p = kzalloc(sizeof(*p), GFP_KERNEL);
> > +	}
>
> Personal preference, but I think an if-elif-else with a single block
> comment would be easier to read.


I can do with that. thanks for your feedback.


> 	/*
> 	 * Blah blah blah
> 	 */
> 	if (cpu < HVC_BOOT_ARRAY_SIZE)
> 		p = &hv_clock_boot[cpu];
> 	else if (sev_active())
> 		p = &hv_clock_dec[cpu - HVC_BOOT_ARRAY_SIZE];
> 	else
> 		p = kzalloc(sizeof(*p), GFP_KERNEL);