On 11/27/24 09:35, Maciej Wieczor-Retman wrote:
> -/* Check 5-level page table feature in CPUID.(EAX=07H, ECX=00H):ECX.[bit 16] */
> static inline int cpu_has_la57(void)
> {
> - unsigned int cpuinfo[4];
> -
> - __cpuid_count(0x7, 0, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
> -
> - return (cpuinfo[2] & (1 << 16));
> + return !system("grep -wq la57 /proc/cpuinfo");
> }
I would rather we find another way.
First, we've documented the behavior a bit in here:
https://docs.kernel.org/arch/x86/cpuinfo.html
The important part is:
"The absence of a flag in /proc/cpuinfo by itself means almost
nothing to an end user."
Even worse, let's say there's a CPU bug and we say define a bug bit:
bugs : spectre_v1 spectre_v2 ... la57_is_broken
How is that grep going to work out? ;)
Could you poke around and see if there is any existing ABI that we can
use to query LA57 support? Maybe one of the things KVM exports, or some
TASK_SIZE_MAX comparisons?
