[xen stable-4.17] cmdline: document and enforce "extra_guest_irqs" upper bounds

[patchbot@xxxxxxx]

commit a626bfbcbb532f5a22182fab0bfbd51597a6a666
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jul 4 14:22:54 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jul 4 14:22:54 2024 +0200

    cmdline: document and enforce "extra_guest_irqs" upper bounds
    
    PHYSDEVOP_pirq_eoi_gmfn_v<N> accepting just a single GFN implies that no
    more than 32k pIRQ-s can be used by a domain on x86. Document this upper
    bound.
    
    To also enforce the limit, (ab)use both arch_hwdom_irqs() (changing its
    parameter type) and setup_system_domains(). This is primarily to avoid
    exposing the two static variables or introducing yet further arch hooks.
    
    While touching arch_hwdom_irqs() also mark it hwdom-init.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    
    amend 'cmdline: document and enforce "extra_guest_irqs" upper bounds'
    
    Address late review comments for what is now commit 17f6d398f765:
    - bound max_irqs right away against nr_irqs
    - introduce a #define for a constant used twice
    
    Requested-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    master commit: 17f6d398f76597f8009ec0530842fb8705ece7ba
    master date: 2024-07-02 12:00:27 +0200
    master commit: 1f56accba33ffea0abf7d1c6384710823d10cbd6
    master date: 2024-07-03 14:03:27 +0200
---
 docs/misc/xen-command-line.pandoc |  3 ++-
 xen/arch/x86/io_apic.c            | 17 ++++++++++-------
 xen/common/domain.c               | 24 ++++++++++++++++++++++--
 xen/include/xen/irq.h             |  3 ++-
 4 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index fba5a8221b..ccb185a4f3 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1141,7 +1141,8 @@ common for all domUs, while the optional second number 
(preceded by a comma)
 is for dom0.  Changing the setting for domU has no impact on dom0 and vice
 versa.  For example to change dom0 without changing domU, use
 `extra_guest_irqs=,512`.  The default value for Dom0 and an eventual separate
-hardware domain is architecture dependent.
+hardware domain is architecture dependent.  The upper limit for both values on
+x86 is such that the resulting total number of IRQs can't be higher than 32768.
 Note that specifying zero as domU value means zero, while for dom0 it means
 to use the default.
 
diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index e3e71c7a52..6f4b04878d 100644
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -2661,18 +2661,21 @@ void __init ioapic_init(void)
            nr_irqs_gsi, nr_irqs - nr_irqs_gsi);
 }
 
-unsigned int arch_hwdom_irqs(domid_t domid)
+unsigned int __hwdom_init arch_hwdom_irqs(const struct domain *d)
 {
     unsigned int n = fls(num_present_cpus());
+    /* Bounding by the domain pirq EOI bitmap capacity. */
+    const unsigned int max_irqs = min_t(unsigned int, nr_irqs,
+                                        PAGE_SIZE * BITS_PER_BYTE);
 
-    if ( !domid )
-        n = min(n, dom0_max_vcpus());
-    n = min(nr_irqs_gsi + n * NR_DYNAMIC_VECTORS, nr_irqs);
+    if ( is_system_domain(d) )
+        return max_irqs;
 
-    /* Bounded by the domain pirq eoi bitmap gfn. */
-    n = min_t(unsigned int, n, PAGE_SIZE * BITS_PER_BYTE);
+    if ( !d->domain_id )
+        n = min(n, dom0_max_vcpus());
+    n = min(nr_irqs_gsi + n * NR_DYNAMIC_VECTORS, max_irqs);
 
-    printk("Dom%d has maximum %u PIRQs\n", domid, n);
+    printk("%pd has maximum %u PIRQs\n", d, n);
 
     return n;
 }
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 8f924d5cdd..13a1674ce4 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -351,7 +351,8 @@ static int late_hwdom_init(struct domain *d)
 }
 
 static unsigned int __read_mostly extra_hwdom_irqs;
-static unsigned int __read_mostly extra_domU_irqs = 32;
+#define DEFAULT_EXTRA_DOMU_IRQS 32U
+static unsigned int __read_mostly extra_domU_irqs = DEFAULT_EXTRA_DOMU_IRQS;
 
 static int __init cf_check parse_extra_guest_irqs(const char *s)
 {
@@ -659,7 +660,7 @@ struct domain *domain_create(domid_t domid,
             d->nr_pirqs = nr_static_irqs + extra_domU_irqs;
         else
             d->nr_pirqs = extra_hwdom_irqs ? nr_static_irqs + extra_hwdom_irqs
-                                           : arch_hwdom_irqs(domid);
+                                           : arch_hwdom_irqs(d);
         d->nr_pirqs = min(d->nr_pirqs, nr_irqs);
 
         radix_tree_init(&d->pirq_tree);
@@ -783,6 +784,25 @@ void __init setup_system_domains(void)
     if ( IS_ERR(dom_xen) )
         panic("Failed to create d[XEN]: %ld\n", PTR_ERR(dom_xen));
 
+#ifdef CONFIG_HAS_PIRQ
+    /* Bound-check values passed via "extra_guest_irqs=". */
+    {
+        unsigned int n = max(arch_hwdom_irqs(dom_xen), nr_static_irqs);
+
+        if ( extra_hwdom_irqs > n - nr_static_irqs )
+        {
+            extra_hwdom_irqs = n - nr_static_irqs;
+            printk(XENLOG_WARNING "hwdom IRQs bounded to %u\n", n);
+        }
+        if ( extra_domU_irqs >
+             max(DEFAULT_EXTRA_DOMU_IRQS, n - nr_static_irqs) )
+        {
+            extra_domU_irqs = n - nr_static_irqs;
+            printk(XENLOG_WARNING "domU IRQs bounded to %u\n", n);
+        }
+    }
+#endif
+
     /*
      * Initialise our DOMID_IO domain.
      * This domain owns I/O pages that are within the range of the page_info
diff --git a/xen/include/xen/irq.h b/xen/include/xen/irq.h
index f69c9ec760..1fcf5a6755 100644
--- a/xen/include/xen/irq.h
+++ b/xen/include/xen/irq.h
@@ -194,8 +194,9 @@ extern irq_desc_t *pirq_spin_lock_irq_desc(
 
 unsigned int set_desc_affinity(struct irq_desc *, const cpumask_t *);
 
+/* When passed a system domain, this returns the maximum permissible value. */
 #ifndef arch_hwdom_irqs
-unsigned int arch_hwdom_irqs(domid_t);
+unsigned int arch_hwdom_irqs(const struct domain *);
 #endif
 
 #ifndef arch_evtchn_bind_pirq
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.17