[xen staging] xen/arm: ffa: Fix is_64bit init

[patchbot@xxxxxxx]

commit 6e8c62d457ab920b2528c3a5381aef8caa1ff357
Author:     Bertrand Marquis <bertrand.marquis@xxxxxxx>
AuthorDate: Mon Dec 15 15:49:20 2025 +0100
Commit:     Julien Grall <julien@xxxxxxx>
CommitDate: Mon Feb 2 21:19:17 2026 +0000

    xen/arm: ffa: Fix is_64bit init
    
    is_64bit_domain(d) is not set during domain_init as the domain field is
    only set when loading the domain image which is done after executing
    domain_init.
    
    Fix the implementation to set is_64bit when version gets negotiated.
    is_64bit is only used during partition_info_get once a domain is added
    in the list of domains having ffa support. It must only be accessed when
    the rwlock is taken (which is the case).
    
    is_64bit must not be used without the rwlock taken and other places in
    the code needing to test 64bit support of the current domain will have
    to use calls to is_64bit_domain instead of the field from now on.
    
    Fixes: 09a201605f99 ("xen/arm: ffa: Introduce VM to VM support")
    Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
    Reviewed-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
---
 xen/arch/arm/tee/ffa.c         | 9 ++++++++-
 xen/arch/arm/tee/ffa_private.h | 5 +++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
index aadd6c21e7..0f6f837378 100644
--- a/xen/arch/arm/tee/ffa.c
+++ b/xen/arch/arm/tee/ffa.c
@@ -180,6 +180,14 @@ static bool ffa_negotiate_version(struct cpu_user_regs 
*regs)
             goto out_handled;
         }
 
+        /*
+         * We cannot set is_64bit during domain init because the field is not
+         * yet initialized.
+         * This field is only used during partinfo_get with the rwlock taken
+         * so there is no ordering issue with guest_vers.
+         */
+        ctx->is_64bit = is_64bit_domain(d);
+
         /*
          * A successful FFA_VERSION call does not freeze negotiation. Guests
          * are allowed to issue multiple FFA_VERSION attempts (e.g. probing
@@ -433,7 +441,6 @@ static int ffa_domain_init(struct domain *d)
 
     ctx->ffa_id = ffa_get_vm_id(d);
     ctx->num_vcpus = d->max_vcpus;
-    ctx->is_64bit = is_64bit_domain(d);
 
     /*
      * ffa_domain_teardown() will be called if ffa_domain_init() returns an
diff --git a/xen/arch/arm/tee/ffa_private.h b/xen/arch/arm/tee/ffa_private.h
index 8ef2143447..96794ecebe 100644
--- a/xen/arch/arm/tee/ffa_private.h
+++ b/xen/arch/arm/tee/ffa_private.h
@@ -344,6 +344,11 @@ struct ffa_ctx {
     /* FF-A Endpoint ID */
     uint16_t ffa_id;
     uint16_t num_vcpus;
+    /*
+     * Must only be accessed with the ffa_ctx_list_rwlock taken as it set
+     * when guest_vers is set and other accesses could see a partially set
+     * value.
+     */
     bool is_64bit;
 
     /*
--
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