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Re: [Xen-devel] [PATCH v2 06/12] xen/gnttab: Pass max_{grant, maptrack}_frames into grant_table_create()



Hi Andrew,

On 08/13/2018 11:01 AM, Andrew Cooper wrote:
... rather than setting the limits up after domain_create() has completed.

This removes all the gnttab infrastructure for calculating the number of dom0
grant frames, opting instead to require the dom0 construction code to pass a
sane value in via the configuration.

In practice, this now means that there is never a partially constructed grant
table for a reference-able domain.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>

v2:
  * Split/rearrange to avoid the post-domain-create error path.
---
  xen/arch/arm/domain_build.c       |  3 ++-
  xen/arch/arm/setup.c              | 12 ++++++++++++
  xen/arch/x86/setup.c              |  3 +++
  xen/common/domain.c               |  3 ++-
  xen/common/grant_table.c          | 16 +++-------------
  xen/include/asm-arm/grant_table.h | 12 ------------
  xen/include/asm-x86/grant_table.h |  5 -----
  xen/include/xen/grant_table.h     |  6 ++----
  8 files changed, 24 insertions(+), 36 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 1351572..737e0f3 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2079,7 +2079,8 @@ static void __init find_gnttab_region(struct domain *d,
       * enough space for a large grant table
       */
      kinfo->gnttab_start = __pa(_stext);
-    kinfo->gnttab_size = gnttab_dom0_frames() << PAGE_SHIFT;
+    kinfo->gnttab_size = min_t(unsigned int, opt_max_grant_frames,
+                               PFN_DOWN(_etext - _stext)) << PAGE_SHIFT;


I agree with Jan's comment on v1 that there is a risk someone will update the size here but ...


#ifdef CONFIG_ARM_32
      /*
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 45f3841..3d3b30c 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -20,6 +20,7 @@
  #include <xen/compile.h>
  #include <xen/device_tree.h>
  #include <xen/domain_page.h>
+#include <xen/grant_table.h>
  #include <xen/types.h>
  #include <xen/string.h>
  #include <xen/serial.h>
@@ -693,6 +694,17 @@ void __init start_xen(unsigned long boot_phys_offset,
      struct domain *dom0;
      struct xen_domctl_createdomain dom0_cfg = {
          .max_evtchn_port = -1,
+
+        /*
+         * The region used by Xen on the memory will never be mapped in DOM0
+         * memory layout. Therefore it can be used for the grant table.
+         *
+         * Only use the text section as it's always present and will contain
+         * enough space for a large grant table
+         */
+        .max_grant_frames = min_t(unsigned int, opt_max_grant_frames,
+                                  PFN_DOWN(_etext - _stext)),

... not here. So I would prefer if we either keep an helper to find the size of pass that size around to domain_build. Do we store the size in the domain information?

Cheers,

--
Julien Grall

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