[xen master] xen/arm: Validate generic timer frequency

[patchbot@xxxxxxx]

commit 9a5bbb2d34ef90ab7d146f11c9c2c0a23fb08035
Author:     Michal Orzel <michal.orzel@xxxxxxx>
AuthorDate: Thu Sep 28 14:34:35 2023 +0200
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Fri Oct 13 09:46:58 2023 +0100

    xen/arm: Validate generic timer frequency
    
    Generic timer dt node property "clock-frequency" (refer Linux dt binding
    Documentation/devicetree/bindings/timer/arm,arch_timer.yaml) is used to
    override the incorrect value set by firmware in CNTFRQ_EL0. If the value
    of this property is 0 (i.e. by mistake), Xen would continue to work and
    use the value from the sysreg instead. The logic is thus incorrect and
    results in inconsistency when creating timer node for domUs:
     - libxl domUs: clock_frequency member of struct xen_arch_domainconfig
       is set to 0 and libxl ignores setting the "clock-frequency" property,
     - dom0less domUs: "clock-frequency" property is taken from dt_host and
       thus set to 0.
    
    Property "clock-frequency" is used to override the value from sysreg,
    so if it is also invalid, there is nothing we can do and we shall panic
    to let user know about incorrect setting. Going even further, we operate
    under assumption that the frequency must be at least 1KHz (i.e. cpu_khz
    not 0) in order for Xen to boot. Therefore, introduce a new helper
    validate_timer_frequency() to verify this assumption and use it to check
    the frequency obtained either from dt property or from sysreg.
    
    Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
    Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
    Release-acked-by: Henry Wang <Henry.Wang@xxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/time.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c
index 3535bd8ac7..04b07096b1 100644
--- a/xen/arch/arm/time.c
+++ b/xen/arch/arm/time.c
@@ -101,6 +101,17 @@ static void __init preinit_acpi_xen_time(void)
 static void __init preinit_acpi_xen_time(void) { }
 #endif
 
+static void __init validate_timer_frequency(void)
+{
+    /*
+     * ARM ARM does not impose any strict limit on the range of allowable
+     * system counter frequencies. However, we operate under the assumption
+     * that cpu_khz must not be 0.
+     */
+    if ( !cpu_khz )
+        panic("Timer frequency is less than 1 KHz\n");
+}
+
 /* Set up the timer on the boot CPU (early init function) */
 static void __init preinit_dt_xen_time(void)
 {
@@ -122,6 +133,7 @@ static void __init preinit_dt_xen_time(void)
     if ( res )
     {
         cpu_khz = rate / 1000;
+        validate_timer_frequency();
         timer_dt_clock_frequency = rate;
     }
 }
@@ -137,7 +149,10 @@ void __init preinit_xen_time(void)
         preinit_acpi_xen_time();
 
     if ( !cpu_khz )
+    {
         cpu_khz = (READ_SYSREG(CNTFRQ_EL0) & CNTFRQ_MASK) / 1000;
+        validate_timer_frequency();
+    }
 
     res = platform_init_time();
     if ( res )
--
generated by git-patchbot for /home/xen/git/xen.git#master