Reduce GPA pool from 1024 to 512 pages for VMM tests (#939)

After updating CI gates to use Rust 1.85 we started to see test errors
which looks like OOM errors.
Unfortunately, weren't reproducible on DevBox testing (both WSL2 and
Windows).
This change will return some reserved memory back to Linux pool in
attempt to see if it can help.
The change can stay permanent because 512 pages is enough to pass the
tests.

Author: yupavlen-ms

openhcl/openhcl_boot/src/cmdline.rs

@@ -161,11 +161,11 @@ mod tests {
             }
         );
         assert_eq!(
-            parse_boot_command_line("OPENHCL_ENABLE_VTL2_GPA_POOL=1024"),
+            parse_boot_command_line("OPENHCL_ENABLE_VTL2_GPA_POOL=512"),
             BootCommandLineOptions {
                 logger: None,
                 confidential_debug: false,
-                enable_vtl2_gpa_pool: Some(1024),
+                enable_vtl2_gpa_pool: Some(512),
             }
         );
     }

vmm_tests/vmm_tests/tests/tests/x86_64/openhcl_servicing.rs

@@ -58,7 +58,7 @@ async fn openhcl_servicing_keepalive(
 ) -> Result<(), anyhow::Error> {
     openhcl_servicing_core(
         config,
-        "OPENHCL_ENABLE_VTL2_GPA_POOL=1024",
+        "OPENHCL_ENABLE_VTL2_GPA_POOL=512",
         igvm_file,
         OpenHclServicingFlags {
             enable_nvme_keepalive: true,

vmm_tests/vmm_tests/tests/tests/x86_64/openhcl_uefi.rs

@@ -83,7 +83,7 @@ async fn nvme_relay_shared_pool(config: PetriVmConfigOpenVmm) -> Result<(), anyh
 #[openvmm_test(openhcl_uefi_x64[nvme](vhd(ubuntu_2204_server_x64)))]
 async fn nvme_relay_private_pool(config: PetriVmConfigOpenVmm) -> Result<(), anyhow::Error> {
     // Number of pages to reserve as a private pool.
-    nvme_relay_test_core(config, "OPENHCL_ENABLE_VTL2_GPA_POOL=1024").await
+    nvme_relay_test_core(config, "OPENHCL_ENABLE_VTL2_GPA_POOL=512").await
 }
 
 /// Servicing test of an OpenHCL uefi VM with a NVME disk assigned to VTL2 that boots
@@ -97,7 +97,7 @@ async fn nvme_keepalive(
 ) -> Result<(), anyhow::Error> {
     nvme_relay_servicing_core(
         config,
-        "OPENHCL_ENABLE_VTL2_GPA_POOL=1024",
+        "OPENHCL_ENABLE_VTL2_GPA_POOL=512",
         igvm_file,
         OpenHclServicingFlags {
             enable_nvme_keepalive: true,