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[Xen-devel] [PATCH v3 5/7] xen/x86: disable global pages for domains with XPTI active



Instead of flushing the TLB from global pages when switching address
spaces with XPTI being active just disable global pages via %cr4
completely when a domain subject to XPTI is active. This avoids the
need for extra TLB flushes as loading %cr3 will remove all TLB
entries.

In order to avoid states with cr3/cr4 having inconsistent values
(e.g. global pages being activated while cr3 already specifies a XPTI
address space) move loading of the new cr4 value to write_ptbase()
(actually to write_cr3_cr4() called by write_ptbase()).

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V3:
- move cr4 loading for all domains from *_ctxt_switch_to() to
  write_cr3_cr4() called by write_ptbase() (Jan Beulich)
- rebase
---
 xen/arch/x86/domain.c          |  5 -----
 xen/arch/x86/flushtlb.c        | 13 ++++++++-----
 xen/arch/x86/mm.c              | 11 ++++++++---
 xen/arch/x86/x86_64/entry.S    | 10 ----------
 xen/common/efi/runtime.c       |  4 ++--
 xen/include/asm-x86/domain.h   |  3 ++-
 xen/include/asm-x86/flushtlb.h |  2 +-
 7 files changed, 21 insertions(+), 27 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 4cac8906ea..fe18d9d3c4 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1520,17 +1520,12 @@ void paravirt_ctxt_switch_from(struct vcpu *v)
 void paravirt_ctxt_switch_to(struct vcpu *v)
 {
     root_pgentry_t *root_pgt = this_cpu(root_pgt);
-    unsigned long cr4;
 
     if ( root_pgt )
         root_pgt[root_table_offset(PERDOMAIN_VIRT_START)] =
             l4e_from_page(v->domain->arch.perdomain_l3_pg,
                           __PAGE_HYPERVISOR_RW);
 
-    cr4 = pv_guest_cr4_to_real_cr4(v);
-    if ( unlikely(cr4 != read_cr4()) )
-        write_cr4(cr4);
-
     if ( unlikely(v->arch.debugreg[7] & DR7_ACTIVE_MASK) )
         activate_debugregs(v);
 
diff --git a/xen/arch/x86/flushtlb.c b/xen/arch/x86/flushtlb.c
index 6345676bc5..d4b8acc837 100644
--- a/xen/arch/x86/flushtlb.c
+++ b/xen/arch/x86/flushtlb.c
@@ -91,20 +91,23 @@ static void do_tlb_flush(void)
     post_flush(t);
 }
 
-void write_cr3(unsigned long cr3)
+void write_cr3_cr4(unsigned long cr3, unsigned long cr4)
 {
-    unsigned long flags, cr4;
+    unsigned long flags;
     u32 t;
 
     /* This non-reentrant function is sometimes called in interrupt context. */
     local_irq_save(flags);
 
     t = pre_flush();
-    cr4 = read_cr4();
 
-    write_cr4(cr4 & ~X86_CR4_PGE);
+    if ( read_cr4() & X86_CR4_PGE )
+        write_cr4(cr4 & ~X86_CR4_PGE);
+
     asm volatile ( "mov %0, %%cr3" : : "r" (cr3) : "memory" );
-    write_cr4(cr4);
+
+    if ( read_cr4() != cr4 )
+        write_cr4(cr4);
 
     post_flush(t);
 
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index e68ed474bf..c2738dd3fd 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -508,18 +508,23 @@ void make_cr3(struct vcpu *v, mfn_t mfn)
 void write_ptbase(struct vcpu *v)
 {
     struct cpu_info *cpu_info = get_cpu_info();
+    unsigned long new_cr4;
+
+    new_cr4 = (is_pv_vcpu(v) && !is_idle_vcpu(v))
+              ? pv_guest_cr4_to_real_cr4(v) : mmu_cr4_features;
 
     if ( is_pv_vcpu(v) && v->domain->arch.pv_domain.xpti )
     {
         cpu_info->root_pgt_changed = true;
         cpu_info->pv_cr3 = __pa(this_cpu(root_pgt));
-        asm volatile ( "mov %0, %%cr3" : : "r" (v->arch.cr3) : "memory" );
+        write_cr3_cr4(v->arch.cr3, new_cr4);
     }
     else
     {
-        /* Make sure to clear xen_cr3 before pv_cr3; write_cr3() serializes. */
+        /* Make sure to clear xen_cr3 before pv_cr3. */
         cpu_info->xen_cr3 = 0;
-        write_cr3(v->arch.cr3);
+        /* write_cr3_cr4() serializes. */
+        write_cr3_cr4(v->arch.cr3, new_cr4);
         cpu_info->pv_cr3 = 0;
     }
 }
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index 2a06cd1a51..eb33ec835a 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -154,13 +154,8 @@ restore_all_guest:
                 ROOT_PAGETABLE_LAST_XEN_SLOT - 1) * 8, %rdi
         rep movsq
 .Lrag_copy_done:
-        mov   STACK_CPUINFO_FIELD(cr4)(%rdx), %rdi
         mov   %r9, STACK_CPUINFO_FIELD(xen_cr3)(%rdx)
-        mov   %rdi, %rsi
-        and   $~X86_CR4_PGE, %rdi
-        mov   %rdi, %cr4
         mov   %rax, %cr3
-        mov   %rsi, %cr4
 .Lrag_cr3_end:
         ALTERNATIVE_NOP .Lrag_cr3_start, .Lrag_cr3_end, X86_FEATURE_NO_XPTI
 
@@ -218,12 +213,7 @@ restore_all_xen:
          * so "g" will have to do.
          */
 UNLIKELY_START(g, exit_cr3)
-        mov   %cr4, %rdi
-        mov   %rdi, %rsi
-        and   $~X86_CR4_PGE, %rdi
-        mov   %rdi, %cr4
         mov   %rax, %cr3
-        mov   %rsi, %cr4
 UNLIKELY_END(exit_cr3)
 .Lrax_cr3_end:
         ALTERNATIVE_NOP .Lrax_cr3_start, .Lrax_cr3_end, X86_FEATURE_NO_XPTI
diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c
index 3dbc2e8ee5..fad8ca9e95 100644
--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -111,7 +111,7 @@ struct efi_rs_state efi_rs_enter(void)
         lgdt(&gdt_desc);
     }
 
-    write_cr3(virt_to_maddr(efi_l4_pgtable));
+    write_cr3_cr4(virt_to_maddr(efi_l4_pgtable), read_cr4());
 
     return state;
 }
@@ -120,7 +120,7 @@ void efi_rs_leave(struct efi_rs_state *state)
 {
     if ( !state->cr3 )
         return;
-    write_cr3(state->cr3);
+    write_cr3_cr4(state->cr3, read_cr4());
     if ( is_pv_vcpu(current) && !is_idle_vcpu(current) )
     {
         struct desc_ptr gdt_desc = {
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index b97a8792e9..ef9e9639fd 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -621,7 +621,8 @@ unsigned long pv_guest_cr4_fixup(const struct vcpu *, 
unsigned long guest_cr4);
             X86_CR4_SMAP | X86_CR4_OSXSAVE |                \
             X86_CR4_FSGSBASE))                              \
       | ((v)->domain->arch.vtsc ? X86_CR4_TSD : 0))         \
-     & ~X86_CR4_DE)
+     & ~(X86_CR4_DE |                                       \
+         ((v)->domain->arch.pv_domain.xpti ? X86_CR4_PGE : 0)))
 #define real_cr4_to_pv_guest_cr4(c)                         \
     ((c) & ~(X86_CR4_PGE | X86_CR4_PSE | X86_CR4_TSD |      \
              X86_CR4_OSXSAVE | X86_CR4_SMEP |               \
diff --git a/xen/include/asm-x86/flushtlb.h b/xen/include/asm-x86/flushtlb.h
index 052f0fa403..1eb9682de4 100644
--- a/xen/include/asm-x86/flushtlb.h
+++ b/xen/include/asm-x86/flushtlb.h
@@ -84,7 +84,7 @@ static inline unsigned long read_cr3(void)
 }
 
 /* Write pagetable base and implicitly tick the tlbflush clock. */
-void write_cr3(unsigned long cr3);
+void write_cr3_cr4(unsigned long cr3, unsigned long cr4);
 
 /* flush_* flag fields: */
  /*
-- 
2.13.6


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