arm64/gcs: Don't call gcs_free() during flush_gcs()

JIRA: https://issues.redhat.com/browse/RHEL-101059

commit d2be327
Author: Mark Brown <[email protected]>
Date: Wed, 11 Jun 2025 17:28:13 +0100

    Currently we call gcs_free() during flush_gcs() to reset the thread
    state for GCS. This includes unmapping any kernel allocated GCS, but
    this is redundant when doing a flush_thread() since we are
    reinitialising the thread memory too. Inline the reinitialisation of the
    thread struct.

    Signed-off-by: Mark Brown <[email protected]>
    Reviewed-by: Catalin Marinas <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]
    Signed-off-by: Will Deacon <[email protected]>

Signed-off-by: Mark Salter <[email protected]>

Author: mosalter

arch/arm64/kernel/process.c

@@ -288,7 +288,9 @@ static void flush_gcs(void)
 	if (!system_supports_gcs())
 		return;
 
-	gcs_free(current);
+	current->thread.gcspr_el0 = 0;
+	current->thread.gcs_base = 0;
+	current->thread.gcs_size = 0;
 	current->thread.gcs_el0_mode = 0;
 	write_sysreg_s(GCSCRE0_EL1_nTR, SYS_GCSCRE0_EL1);
 	write_sysreg_s(0, SYS_GCSPR_EL0);