[Xen-devel] [PATCH v3 4/6] xen/arm: set VPIDR based on the MIDR value of the underlying pCPU

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On big.LITTLE systems not all cores have the same MIDR. Instead of
storing only one VPIDR per domain, initialize it to the value of the
MIDR of the pCPU where the vCPU will run.

This way, assuming that the vCPU has been created with the right pCPU
affinity, the guest will be able to read the right VPIDR value, matching
the one of the physical cpu.

Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

---

Changes in v3:
- improve commit message
- do not store vpidr in struct vcpu

Changes in v2:
- remove warning message
- make vpidr per vcpu
---
 xen/arch/arm/domain.c        | 8 ++++----
 xen/arch/arm/vcpreg.c        | 4 ++--
 xen/include/asm-arm/domain.h | 3 ---
 3 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 5e76809..545bbf6 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -172,6 +172,8 @@ static void ctxt_switch_from(struct vcpu *p)
 
 static void ctxt_switch_to(struct vcpu *n)
 {
+    uint32_t vpidr;
+
     /* When the idle VCPU is running, Xen will always stay in hypervisor
      * mode. Therefore we don't need to restore the context of an idle VCPU.
      */
@@ -180,7 +182,8 @@ static void ctxt_switch_to(struct vcpu *n)
 
     p2m_restore_state(n);
 
-    WRITE_SYSREG32(n->domain->arch.vpidr, VPIDR_EL2);
+    vpidr = READ_SYSREG32(MIDR_EL1);
+    WRITE_SYSREG32(vpidr, VPIDR_EL2);
     WRITE_SYSREG(n->arch.vmpidr, VMPIDR_EL2);
 
     /* VGIC */
@@ -595,9 +598,6 @@ int arch_domain_create(struct domain *d, unsigned int 
domcr_flags,
     if ( (d->shared_info = alloc_xenheap_pages(0, 0)) == NULL )
         goto fail;
 
-    /* Default the virtual ID to match the physical */
-    d->arch.vpidr = boot_cpu_data.midr.bits;
-
     clear_page(d->shared_info);
     share_xen_page_with_guest(
         virt_to_page(d->shared_info), d, XENSHARE_writable);
diff --git a/xen/arch/arm/vcpreg.c b/xen/arch/arm/vcpreg.c
index e363183..b04d996 100644
--- a/xen/arch/arm/vcpreg.c
+++ b/xen/arch/arm/vcpreg.c
@@ -230,7 +230,6 @@ void do_cp14_32(struct cpu_user_regs *regs, const union hsr 
hsr)
 {
     const struct hsr_cp32 cp32 = hsr.cp32;
     int regidx = cp32.reg;
-    struct domain *d = current->domain;
 
     if ( !check_conditional_instr(regs, hsr) )
     {
@@ -295,7 +294,8 @@ void do_cp14_32(struct cpu_user_regs *regs, const union hsr 
hsr)
          *  - Variant and Revision bits match MDIR
          */
         val = (1 << 24) | (5 << 16);
-        val |= ((d->arch.vpidr >> 20) & 0xf) | (d->arch.vpidr & 0xf);
+        val |= ((current_cpu_data.midr.bits >> 20) & 0xf) |
+                (current_cpu_data.midr.bits & 0xf);
         set_user_reg(regs, regidx, val);
 
         break;
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index 4fe189b..0dd8c95 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -63,9 +63,6 @@ struct arch_domain
         RELMEM_done,
     } relmem;
 
-    /* Virtual CPUID */
-    uint32_t vpidr;
-
     struct {
         uint64_t offset;
     } phys_timer_base;
-- 
1.9.1


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