On 09/06/2018 03:39 PM, Sean Christopherson wrote:
On Thu, Sep 06, 2018 at 03:20:46PM -0500, Brijesh Singh wrote:
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.
Hmm, we'll need something otherwise 'NR_CPUS - HVC_BOOT_ARRAY_SIZE'
will wrap and cause build errors.
Right.
One option is we can hard-code the check for > 64, something like this:
#if defined(CONFIG_AMD_MEM_ENCRYPT) && NR_CPUS > 64
...
...
#endif
But this assumption will break if we ever add a new field in
struct pvclock_vsyscall_time_info. Hence I am not in favor of this.
Second option is, use KVM_MAX_VCPUS or NR_CPUS, something like this:
#ifdef CONFIG_AMD_MEM_ENCRYPT
#define HVC_AUX_ARRAY_SIZE \
PAGE_ALIGN(NR_CPUS * sizeof(struct pvclock_vsyscall_time_info))
...
#endif
In this case we will allocate few extra bytes which will get freed for
the non-SEV case anyways.
