[xen stable-4.16] libxl, docs: Use arch-specific default paging memory

[patchbot@xxxxxxx]

commit 755a9b52844de3e1e47aa1fc9991a4240ccfbf35
Author:     Henry Wang <Henry.Wang@xxxxxxx>
AuthorDate: Tue Oct 11 14:55:08 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 11 14:55:08 2022 +0200

    libxl, docs: Use arch-specific default paging memory
    
    The default paging memory (descibed in `shadow_memory` entry in xl
    config) in libxl is used to determine the memory pool size for xl
    guests. Currently this size is only used for x86, and contains a part
    of RAM to shadow the resident processes. Since on Arm there is no
    shadow mode guests, so the part of RAM to shadow the resident processes
    is not necessary. Therefore, this commit splits the function
    `libxl_get_required_shadow_memory()` to arch specific helpers and
    renamed the helper to `libxl__arch_get_required_paging_memory()`.
    
    On x86, this helper calls the original value from
    `libxl_get_required_shadow_memory()` so no functional change intended.
    
    On Arm, this helper returns 1MB per vcpu plus 4KB per MiB of RAM
    for the P2M map and additional 512KB.
    
    Also update the xl.cfg documentation to add Arm documentation
    according to code changes and correct the comment style following Xen
    coding style.
    
    This is part of CVE-2022-33747 / XSA-409.
    
    Suggested-by: Julien Grall <jgrall@xxxxxxxxxx>
    Signed-off-by: Henry Wang <Henry.Wang@xxxxxxx>
    Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    master commit: 156a239ea288972425f967ac807b3cb5b5e14874
    master date: 2022-10-11 14:28:37 +0200
---
 docs/man/xl.cfg.5.pod.in       |  5 +++++
 tools/libs/light/libxl_arch.h  |  4 ++++
 tools/libs/light/libxl_arm.c   | 14 ++++++++++++++
 tools/libs/light/libxl_utils.c |  9 ++-------
 tools/libs/light/libxl_x86.c   | 13 +++++++++++++
 5 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
index b98d161398..eda1e77ebd 100644
--- a/docs/man/xl.cfg.5.pod.in
+++ b/docs/man/xl.cfg.5.pod.in
@@ -1768,6 +1768,11 @@ are not using hardware assisted paging (i.e. you are 
using shadow
 mode) and your guest workload consists of a very large number of
 similar processes then increasing this value may improve performance.
 
+On Arm, this field is used to determine the size of the guest P2M pages
+pool, and the default value is 1MB per vCPU plus 4KB per MB of RAM for
+the P2M map and additional 512KB for extended regions. Users should
+adjust this value if bigger P2M pool size is needed.
+
 =back
 
 =head3 Processor and Platform Features
diff --git a/tools/libs/light/libxl_arch.h b/tools/libs/light/libxl_arch.h
index 1522ecb97f..5a060c2c30 100644
--- a/tools/libs/light/libxl_arch.h
+++ b/tools/libs/light/libxl_arch.h
@@ -90,6 +90,10 @@ void libxl__arch_update_domain_config(libxl__gc *gc,
                                       libxl_domain_config *dst,
                                       const libxl_domain_config *src);
 
+_hidden
+unsigned long libxl__arch_get_required_paging_memory(unsigned long maxmem_kb,
+                                                     unsigned int smp_cpus);
+
 #if defined(__i386__) || defined(__x86_64__)
 
 #define LAPIC_BASE_ADDRESS  0xfee00000
diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
index eef1de0939..73a95e83af 100644
--- a/tools/libs/light/libxl_arm.c
+++ b/tools/libs/light/libxl_arm.c
@@ -154,6 +154,20 @@ out:
     return rc;
 }
 
+unsigned long libxl__arch_get_required_paging_memory(unsigned long maxmem_kb,
+                                                     unsigned int smp_cpus)
+{
+    /*
+     * 256 pages (1MB) per vcpu,
+     * plus 1 page per MiB of RAM for the P2M map,
+     * plus 1 page per MiB of extended region. This default value is 128 MiB
+     * which should be enough for domains that are not running backend.
+     * This is higher than the minimum that Xen would allocate if no value
+     * were given (but the Xen minimum is for safety, not performance).
+     */
+    return 4 * (256 * smp_cpus + maxmem_kb / 1024 + 128);
+}
+
 static struct arch_info {
     const char *guest_type;
     const char *timer_compat;
diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
index 4699c4a0a3..e276c0ee9c 100644
--- a/tools/libs/light/libxl_utils.c
+++ b/tools/libs/light/libxl_utils.c
@@ -18,6 +18,7 @@
 #include <ctype.h>
 
 #include "libxl_internal.h"
+#include "libxl_arch.h"
 #include "_paths.h"
 
 #ifndef LIBXL_HAVE_NONCONST_LIBXL_BASENAME_RETURN_VALUE
@@ -39,13 +40,7 @@ char *libxl_basename(const char *name)
 
 unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, 
unsigned int smp_cpus)
 {
-    /* 256 pages (1MB) per vcpu,
-       plus 1 page per MiB of RAM for the P2M map,
-       plus 1 page per MiB of RAM to shadow the resident processes.
-       This is higher than the minimum that Xen would allocate if no value
-       were given (but the Xen minimum is for safety, not performance).
-     */
-    return 4 * (256 * smp_cpus + 2 * (maxmem_kb / 1024));
+    return libxl__arch_get_required_paging_memory(maxmem_kb, smp_cpus);
 }
 
 char *libxl_domid_to_name(libxl_ctx *ctx, uint32_t domid)
diff --git a/tools/libs/light/libxl_x86.c b/tools/libs/light/libxl_x86.c
index 1feadebb18..51362893cf 100644
--- a/tools/libs/light/libxl_x86.c
+++ b/tools/libs/light/libxl_x86.c
@@ -882,6 +882,19 @@ void libxl__arch_update_domain_config(libxl__gc *gc,
                     libxl_defbool_val(src->b_info.arch_x86.msr_relaxed));
 }
 
+unsigned long libxl__arch_get_required_paging_memory(unsigned long maxmem_kb,
+                                                     unsigned int smp_cpus)
+{
+    /*
+     * 256 pages (1MB) per vcpu,
+     * plus 1 page per MiB of RAM for the P2M map,
+     * plus 1 page per MiB of RAM to shadow the resident processes.
+     * This is higher than the minimum that Xen would allocate if no value
+     * were given (but the Xen minimum is for safety, not performance).
+     */
+    return 4 * (256 * smp_cpus + 2 * (maxmem_kb / 1024));
+}
+
 /*
  * Local variables:
  * mode: C
--
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