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

[Brijesh Singh]

On 09/06/2018 02:24 PM, Brijesh Singh wrote:

...

> > > Again we have to consider the bare metal scenario while doing this. The
> > > aux array you proposed will be added in decrypted section only when
> > > CONFIG_AMD_MEM_ENCRYPT=y. If CONFIG_AMD_MEM_ENCRYPT=n then nothng
> > > gets put in .data.decrypted section. At the runtime, if memory
> > > encryption is active then .data.decrypted_hvclock will contains useful
> > > data.
> > >
> > > The __decrypted attribute in "" when CONFIG_AMD_MEM_ENCRYPT=n.
> >
> > Right, but won't the data get dumped into the regular .bss in that
> > case, i.e. needs to be freed?
>
>
> 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.

We can use #ifdef CONFIG_AMD_MEM_ENCRYPT around hv_clock_aux definition
so that it gets defined

Something like this:

#ifdef CONFIG_AMD_MEM_ENCRYPT
/* The auxilary array will be used when SEV is active */
#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_aux;
#endif