OvmfPkg/PlatformInitLib: factor out PlatformCpuCountBugCheck()

Move the QEMU v2.7 reset bug check/workaround to a separate function, as
we'll need to detect further issues.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Michael Brown <mcb30@ipxe.org>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Oliver Steffen <osteffen@redhat.com>
Cc: Sebastien Boeuf <sebastien.boeuf@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=4250
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20230119110131.91923-2-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Hugely-appreciated-by: Michael Brown <mcb30@ipxe.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 58 insertions, 23 deletions

diff --git a/OvmfPkg/Library/PlatformInitLib/Platform.c b/OvmfPkg/Library/PlatformInitLib/Platform.c
index 9ab0342fd8..d1be5c2d79 100644
--- a/OvmfPkg/Library/PlatformInitLib/Platform.c
+++ b/OvmfPkg/Library/PlatformInitLib/Platform.c
@@ -405,6 +405,61 @@ PlatformMiscInitialization (
 }

 

 /**

+  Check for various QEMU bugs concerning CPU numbers.

+

+  Compensate for those bugs if various conditions are satisfied, by updating a

+  suitable subset of the input-output parameters. The function may not return

+  (it may hang deliberately), even in RELEASE builds, if the QEMU bug is

+  impossible to cover up.

+

+  @param[in,out] BootCpuCount  On input, the boot CPU count reported by QEMU via

+                               fw_cfg (QemuFwCfgItemSmpCpuCount). The caller is

+                               responsible for ensuring (BootCpuCount > 0); that

+                               is, if QEMU does not provide the boot CPU count

+                               via fw_cfg *at all*, then this function must not

+                               be called.

+

+  @param[in,out] Present       On input, the number of present-at-boot CPUs, as

+                               reported by QEMU through the modern CPU hotplug

+                               register block.

+

+  @param[in,out] Possible      On input, the number of possible CPUs, as

+                               reported by QEMU through the modern CPU hotplug

+                               register block.

+**/

+STATIC

+VOID

+PlatformCpuCountBugCheck (

+  IN OUT UINT16  *BootCpuCount,

+  IN OUT UINT32  *Present,

+  IN OUT UINT32  *Possible

+  )

+{

+  ASSERT (*BootCpuCount > 0);

+

+  //

+  // Sanity check: fw_cfg and the modern CPU hotplug interface should expose the

+  // same boot CPU count.

+  //

+  if (*BootCpuCount != *Present) {

+    DEBUG ((

+      DEBUG_WARN,

+      "%a: QEMU v2.7 reset bug: BootCpuCount=%d Present=%u\n",

+      __FUNCTION__,

+      *BootCpuCount,

+      *Present

+      ));

+    //

+    // The handling of QemuFwCfgItemSmpCpuCount, across CPU hotplug plus

+    // platform reset (including S3), was corrected in QEMU commit e3cadac073a9

+    // ("pc: fix FW_CFG_NB_CPUS to account for -device added CPUs", 2016-11-16),

+    // part of release v2.8.0.

+    //

+    *BootCpuCount = (UINT16)*Present;

+  }

+}

+

+/**

   Fetch the boot CPU count and the possible CPU count from QEMU, and expose

   them to UefiCpuPkg modules.

 **/

@@ -518,8 +573,8 @@ PlatformMaxCpuCountInitialization (
         UINT8  CpuStatus;

 

         //

-        // Read the status of the currently selected CPU. This will help with a

-        // sanity check against "BootCpuCount".

+        // Read the status of the currently selected CPU. This will help with

+        // various CPU count sanity checks.

         //

         CpuStatus = IoRead8 (CpuHpBase + QEMU_CPUHP_R_CPU_STAT);

         if ((CpuStatus & QEMU_CPUHP_STAT_ENABLED) != 0) {

@@ -540,27 +595,7 @@ PlatformMaxCpuCountInitialization (
         ASSERT (Selected == Possible || Selected == 0);

       } while (Selected > 0);

 

-      //

-      // Sanity check: fw_cfg and the modern CPU hotplug interface should

-      // return the same boot CPU count.

-      //

-      if (BootCpuCount != Present) {

-        DEBUG ((

-          DEBUG_WARN,

-          "%a: QEMU v2.7 reset bug: BootCpuCount=%d "

-          "Present=%u\n",

-          __FUNCTION__,

-          BootCpuCount,

-          Present

-          ));

-        //

-        // The handling of QemuFwCfgItemSmpCpuCount, across CPU hotplug plus

-        // platform reset (including S3), was corrected in QEMU commit

-        // e3cadac073a9 ("pc: fix FW_CFG_NB_CPUS to account for -device added

-        // CPUs", 2016-11-16), part of release v2.8.0.

-        //

-        BootCpuCount = (UINT16)Present;

-      }

+      PlatformCpuCountBugCheck (&BootCpuCount, &Present, &Possible);

 

       MaxCpuCount = Possible;

     }