[xen staging-4.13] libxl, docs: Use arch-specific default paging memory

[patchbot@xxxxxxx]

commit 9992c089de1fbb4d3217d2421ca60295998645d7
Author:     Henry Wang <Henry.Wang@xxxxxxx>
AuthorDate: Tue Oct 11 15:51:26 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 11 15:51:26 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/libxl/libxl_arch.h  |  4 ++++
 tools/libxl/libxl_arm.c   | 12 ++++++++++++
 tools/libxl/libxl_utils.c |  9 ++-------
 tools/libxl/libxl_x86.c   | 12 ++++++++++++
 5 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
index 245d3f9472..3b297c6a97 100644
--- a/docs/man/xl.cfg.5.pod.in
+++ b/docs/man/xl.cfg.5.pod.in
@@ -1790,6 +1790,11 @@ 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. Users should adjust this value if bigger P2M pool size is
+needed.
+
 =back
 
 =head3 Processor and Platform Features
diff --git a/tools/libxl/libxl_arch.h b/tools/libxl/libxl_arch.h
index 6a91775b9e..b09f868490 100644
--- a/tools/libxl/libxl_arch.h
+++ b/tools/libxl/libxl_arch.h
@@ -83,6 +83,10 @@ int libxl__arch_extra_memory(libxl__gc *gc,
                              const libxl_domain_build_info *info,
                              uint64_t *out);
 
+_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/libxl/libxl_arm.c b/tools/libxl/libxl_arm.c
index 34f8a29056..f4b3dc8e71 100644
--- a/tools/libxl/libxl_arm.c
+++ b/tools/libxl/libxl_arm.c
@@ -153,6 +153,18 @@ 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,
+     * 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);
+}
+
 static struct arch_info {
     const char *guest_type;
     const char *timer_compat;
diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index b039143b8a..e18b1524ef 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/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/libxl/libxl_x86.c b/tools/libxl/libxl_x86.c
index f34c0edc10..348876e5c0 100644
--- a/tools/libxl/libxl_x86.c
+++ b/tools/libxl/libxl_x86.c
@@ -681,6 +681,18 @@ int libxl__arch_passthrough_mode_setdefault(libxl__gc *gc,
     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 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:
--
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