Re: [PATCH v3 1/4] xen/arm/static-shmem: Static-shmem should be direct-mapped for direct-mapped domains

[Henry Wang]

Hi Michal,

On 5/20/2024 11:46 PM, Michal Orzel wrote:
Hi Henry,
On 20/05/2024 16:52, Henry Wang wrote:
Hi Michal, Luca,

On 5/20/2024 7:24 PM, Michal Orzel wrote:
Hi Henry,

+CC: Luca

On 17/05/2024 05:21, Henry Wang wrote:
To make things easier, add restriction that static shared memory
should also be direct-mapped for direct-mapped domains. Check the
host physical address to be matched with guest physical address when
parsing the device tree. Document this restriction in the doc.
I'm ok with this restriction.

@Luca, do you have any use case preventing us from making this restriction?

This patch clashes with Luca series so depending on which goes first,
I agree that there will be some conflicts between the two series. To
avoid back and forth, if Luca's series goes in first, would it be ok for
you if I place the same check from this patch in
handle_shared_mem_bank() like below?

diff --git a/xen/arch/arm/static-shmem.c b/xen/arch/arm/static-shmem.c
index 9c3a83042d..2d23fa4917 100644
--- a/xen/arch/arm/static-shmem.c
+++ b/xen/arch/arm/static-shmem.c
@@ -219,6 +219,13 @@ static int __init handle_shared_mem_bank(struct
domain *d, paddr_t gbase,
       pbase = shm_bank->start;
       psize = shm_bank->size;

+    if ( is_domain_direct_mapped(d) && (pbase != gbase) )
+    {
+        printk("%pd: physical address 0x%"PRIpaddr" and guest address
0x%"PRIpaddr" are not direct-mapped.\n",
+               d, pbase, gbase);
+        return -EINVAL;
+    }
+
       printk("%pd: SHMEM map from %s: mphys 0x%"PRIpaddr" -> gphys
0x%"PRIpaddr", size 0x%"PRIpaddr"\n",
              d, bank_from_heap ? "Xen heap" : "Host", pbase, gbase, psize);

Acked-by: Michal Orzel <michal.or...@amd.com>
Thanks. I will take the tag if you are ok with above diff (for the case
if this series goes in later than Luca's).
I would move this check to process_shm() right after "gbase = dt_read_paddr" 
setting.
This would be the most natural placement for such a check.

That sounds good. Thanks! IIUC we only need to add the check for the 
pbase != INVALID_PADDR case correct?

Kind regards,
Henry

~Michal