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

[Brijesh Singh]

On 09/06/2018 02:47 PM, Sean Christopherson wrote:
...

> > Yes, the auxiliary array will dumped into the regular .bss when
> > CONFIG_AMD_MEM_ENCRYPT=n. Typically it will be few k, I am not
> > sure if its worth complicating the code to save those extra memory.
> > Most of the distro's have CONFIG_AMD_MEM_ENCRYPT=y anyways.
>
> I just realized that we'll try to create a bogus array if 'NR_CPUS <=
> HVC_BOOT_ARRAY_SIZE'.  A bit ugly, but we could #ifdef away both that
> and CONFIG_AMD_MEM_ENCRYPT=n in a single shot, e.g.:
>
> #if defined(CONFIG_AMD_MEM_ENCRYPT) && NR_CPUS > HVC_BOOT_ARRAY_SIZE
> #define HVC_AUX_ARRAY_SIZE  \
> 	PAGE_ALIGN((NR_CPUS - HVC_BOOT_ARRAY_SIZE) * \
> 		   sizeof(struct pvclock_vsyscall_time_info))
> static struct pvclock_vsyscall_time_info
> 	hv_clock_aux[HVC_AUX_ARRAY_SIZE] __decrypted __aligned(PAGE_SIZE);
> #endif

The HVC_BOOT_ARRAY_SIZE macro uses sizeof(..) and to my understanding
the sizeof operators are not allowed in '#if'. Anyway, I will try to see
if it can be used, if not then I will stick to CONFIG_AMD_MEM_ENCRYPT
check.

-Brijesh