From 5c81d260c244026ea74632faa3c6d0a00cc76469 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Thu, 26 Apr 2018 13:33:18 +0200
Subject: [PATCH] xen/x86: use PCID feature

Avoid flushing the complete TLB when switching %cr3 for mitigation of
Meltdown by using the PCID feature if available.

We are using 4 PCID values for a 64 bit pv domain subject to XPTI and
2 values for the non-XPTI case:

- guest active and in kernel mode
- guest active and in user mode
- hypervisor active and guest in user mode (XPTI only)
- hypervisor active and guest in kernel mode (XPTI only)

We use PCID only if PCID _and_ INVPCID are supported. With PCID in use
we disable global pages in cr4. A command line parameter controls in
which cases PCID is being used.

As the non-XPTI case has shown not to perform better with PCID at least
on some machines the default is to use PCID only for domains subject to
XPTI.

With PCID enabled we always disable global pages. This avoids having to
either flush the complete TLB or do a cycle through all PCID values
when invalidating a single global page.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -893,7 +893,21 @@ This option can be specified more than o
 
 ### ple\_window
 > `= <integer>`
-	
+
+### pcid (x86)
+> `= <boolean> | xpti=<bool>`
+
+> Default: `xpti`
+
+> Can be modified at runtime (change takes effect only for domains created
+  afterwards)
+
+If available, control usage of the PCID feature of the processor for
+64-bit pv-domains. PCID can be used either for no domain at all (`false`),
+for all of them (`true`), only for those subject to XPTI (`xpti`) or for
+those not subject to XPTI (`no-xpti`). The feature is used only in case
+INVPCID is supported and not disabled via `invpcid=false`.
+
 ### pv-linear-pt
 > `= <boolean>`
 
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -45,7 +45,9 @@
 #include <asm/desc.h>
 #include <asm/i387.h>
 #include <asm/xstate.h>
+#include <asm/cpufeature.h>
 #include <asm/cpuidle.h>
+#include <asm/invpcid.h>
 #include <asm/mpspec.h>
 #include <asm/ldt.h>
 #include <asm/fixmap.h>
@@ -63,6 +65,49 @@
 #include <compat/vcpu.h>
 #include <asm/spec_ctrl.h>
 
+static __read_mostly enum {
+    PCID_OFF,
+    PCID_ALL,
+    PCID_XPTI,
+    PCID_NOXPTI
+} opt_pcid = PCID_XPTI;
+
+static __init int parse_pcid(const char *s)
+{
+    int rc = 0;
+
+    switch ( parse_bool(s) )
+    {
+    case 0:
+        opt_pcid = PCID_OFF;
+        break;
+
+    case 1:
+        opt_pcid = PCID_ALL;
+        break;
+
+    default:
+        switch ( parse_boolean("xpti", s, NULL) )
+        {
+        case 0:
+            opt_pcid = PCID_NOXPTI;
+            break;
+
+        case 1:
+            opt_pcid = PCID_XPTI;
+            break;
+
+        default:
+            rc = -EINVAL;
+            break;
+        }
+        break;
+    }
+
+    return rc;
+}
+custom_param("pcid", parse_pcid);
+
 DEFINE_PER_CPU(struct vcpu *, curr_vcpu);
 DEFINE_PER_CPU(unsigned long, cr4);
 
@@ -342,10 +387,38 @@ static void release_compat_l4(struct vcp
 static void set_domain_xpti(struct domain *d)
 {
     if ( is_pv_32bit_domain(d) )
+    {
         d->arch.pv_domain.xpti = 0;
+        d->arch.pv_domain.pcid = 0;
+    }
     else
+    {
         d->arch.pv_domain.xpti = opt_xpti & (is_hardware_domain(d)
                                              ? OPT_XPTI_DOM0 : OPT_XPTI_DOMU);
+
+        if ( use_invpcid && cpu_has_pcid )
+            switch ( opt_pcid )
+            {
+            case PCID_OFF:
+                break;
+
+            case PCID_ALL:
+                d->arch.pv_domain.pcid = 1;
+                break;
+
+            case PCID_XPTI:
+                d->arch.pv_domain.pcid = d->arch.pv_domain.xpti;
+                break;
+
+            case PCID_NOXPTI:
+                d->arch.pv_domain.pcid = !d->arch.pv_domain.xpti;
+                break;
+
+            default:
+                ASSERT_UNREACHABLE();
+                break;
+            }
+    }
 }
 
 static inline int may_switch_mode(struct domain *d)
--- a/xen/arch/x86/domain_build.c
+++ b/xen/arch/x86/domain_build.c
@@ -433,6 +433,7 @@ int __init construct_dom0(
     {
         d->arch.is_32bit_pv = d->arch.has_32bit_shinfo = 1;
         d->arch.pv_domain.xpti = 0;
+        d->arch.pv_domain.pcid = 0;
         v->vcpu_info = (void *)&d->shared_info->compat.vcpu_info[0];
         if ( setup_compat_arg_xlat(v) != 0 )
             BUG();
@@ -776,7 +777,7 @@ int __init construct_dom0(
         update_cr3(v);
 
     /* We run on dom0's page tables for the final part of the build process. */
-    switch_cr3_cr4(v->arch.cr3, read_cr4());
+    switch_cr3_cr4(cr3_pa(v->arch.cr3), read_cr4());
     mapcache_override_current(v);
 
     /* Copy the OS image and free temporary buffer. */
--- a/xen/arch/x86/flushtlb.c
+++ b/xen/arch/x86/flushtlb.c
@@ -14,6 +14,8 @@
 #include <asm/flushtlb.h>
 #include <asm/invpcid.h>
 #include <asm/page.h>
+#include <asm/domain.h>
+#include <asm/spec_ctrl.h>
 
 /* Debug builds: Wrap frequently to stress-test the wrap logic. */
 #ifdef NDEBUG
@@ -95,6 +97,7 @@ void switch_cr3_cr4(unsigned long cr3, u
 {
     unsigned long flags;
     u32 t;
+    unsigned long old_pcid = cr3_pcid(read_cr3());
 
     /* This non-reentrant function is sometimes called in interrupt context. */
     local_irq_save(flags);
@@ -107,14 +110,35 @@ void switch_cr3_cr4(unsigned long cr3, u
 
         if ( old_cr4 & X86_CR4_PGE )
         {
+            /*
+             * X86_CR4_PGE set means PCID is inactive.
+             * We have to purge the TLB via flipping cr4.pge.
+             */
             old_cr4 = cr4 & ~X86_CR4_PGE;
             write_cr4(old_cr4);
         }
+        else if ( use_invpcid )
+            /*
+             * Flushing the TLB via INVPCID is necessary only in case PCIDs
+             * are in use, which is true only with INVPCID being available.
+             * Without PCID usage the following write_cr3() will purge the TLB
+             * (we are in the cr4.pge off path) of all entries.
+             * Using invpcid_flush_all_nonglobals() seems to be faster than
+             * invpcid_flush_all(), so use that.
+             */
+            invpcid_flush_all_nonglobals();
 
         write_cr3(cr3);
 
         if ( old_cr4 != cr4 )
             write_cr4(cr4);
+        else if ( old_pcid != cr3_pcid(cr3) )
+            /*
+             * Make sure no TLB entries related to the old PCID created
+             * between flushing the TLB and writing the new %cr3 value remain
+             * in the TLB.
+             */
+            invpcid_flush_single_context(old_pcid);
     }
 #else
     write_cr3(cr3);
@@ -146,8 +170,29 @@ void flush_area_local(const void *va, un
              * are various errata surrounding INVLPG usage on superpages, and
              * a full flush is in any case not *that* expensive.
              */
-            asm volatile ( "invlpg %0"
-                           : : "m" (*(const char *)(va)) : "memory" );
+            if ( read_cr4() & X86_CR4_PCIDE )
+            {
+                unsigned long addr = (unsigned long)va;
+
+                /*
+                 * Flush the addresses for all potential address spaces.
+                 * We can't check the current domain for being subject to
+                 * XPTI as current might be the idle vcpu while we still have
+                 * some XPTI domain TLB entries.
+                 * Using invpcid is okay here, as with PCID enabled we always
+                 * have global pages disabled.
+                 */
+                invpcid_flush_one(PCID_PV_PRIV, addr);
+                invpcid_flush_one(PCID_PV_USER, addr);
+                if ( opt_xpti )
+                {
+                    invpcid_flush_one(PCID_PV_PRIV | PCID_PV_XPTI, addr);
+                    invpcid_flush_one(PCID_PV_USER | PCID_PV_XPTI, addr);
+                }
+            }
+            else
+                asm volatile ( "invlpg %0"
+                               : : "m" (*(const char *)(va)) : "memory" );
         }
         else
         {
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -493,7 +493,11 @@ void share_xen_page_with_privileged_gues
 
 void make_cr3(struct vcpu *v, unsigned long mfn)
 {
+    struct domain *d = v->domain;
+
     v->arch.cr3 = mfn << PAGE_SHIFT;
+    if ( is_pv_domain(d) && d->arch.pv_domain.pcid )
+        v->arch.cr3 |= get_pcid_bits(v, 0);
 }
 
 unsigned long pv_guest_cr4_to_real_cr4(const struct vcpu *v)
@@ -504,7 +508,12 @@ unsigned long pv_guest_cr4_to_real_cr4(c
     cr4 = v->arch.pv_vcpu.ctrlreg[4] & ~X86_CR4_DE;
     cr4 |= mmu_cr4_features & (X86_CR4_PSE | X86_CR4_SMEP |
                                X86_CR4_OSXSAVE | X86_CR4_FSGSBASE);
-    cr4 |= d->arch.pv_domain.xpti  ? 0 : X86_CR4_PGE;
+
+    if ( d->arch.pv_domain.pcid )
+        cr4 |= X86_CR4_PCIDE;
+    else if ( !d->arch.pv_domain.xpti )
+        cr4 |= X86_CR4_PGE;
+
     cr4 |= d->arch.vtsc ? X86_CR4_TSD : 0;
 
     return cr4;
@@ -517,12 +526,14 @@ void write_ptbase(struct vcpu *v)
 
     new_cr4 = (is_pv_vcpu(v) && !is_idle_vcpu(v))
               ? pv_guest_cr4_to_real_cr4(v)
-              : ((read_cr4() & ~X86_CR4_TSD) | X86_CR4_PGE);
+              : ((read_cr4() & ~(X86_CR4_PCIDE | X86_CR4_TSD)) | X86_CR4_PGE);
 
     if ( is_pv_vcpu(v) && v->domain->arch.pv_domain.xpti )
     {
         cpu_info->root_pgt_changed = 1;
         cpu_info->pv_cr3 = __pa(this_cpu(root_pgt));
+        if ( new_cr4 & X86_CR4_PCIDE )
+            cpu_info->pv_cr3 |= get_pcid_bits(v, 1);
         switch_cr3_cr4(v->arch.cr3, new_cr4);
     }
     else
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -280,12 +280,22 @@ void toggle_guest_mode(struct vcpu *v)
 
 void toggle_guest_pt(struct vcpu *v)
 {
+    const struct domain *d = v->domain;
+
     if ( is_pv_32bit_vcpu(v) )
         return;
 
     v->arch.flags ^= TF_kernel_mode;
     update_cr3(v);
-    get_cpu_info()->root_pgt_changed = 1;
+    if ( d->arch.pv_domain.xpti )
+    {
+        struct cpu_info *cpu_info = get_cpu_info();
+
+        cpu_info->root_pgt_changed = 1;
+        cpu_info->pv_cr3 = __pa(this_cpu(root_pgt)) |
+                           (d->arch.pv_domain.pcid
+                            ? get_pcid_bits(v, 1) : 0);
+    }
 
 #ifdef USER_MAPPINGS_ARE_GLOBAL
     /* Don't flush user global mappings from the TLB. Don't tick TLB clock. */
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -253,11 +253,42 @@ struct pv_domain
 
     /* XPTI active? */
     bool_t xpti;
+    /* Use PCID feature? */
+    bool_t pcid;
 
     /* map_domain_page() mapping cache. */
     struct mapcache_domain mapcache;
 };
 
+/*
+ * PCID values for the address spaces of 64-bit pv domains:
+ *
+ * We are using 4 PCID values for a 64 bit pv domain subject to XPTI:
+ * - hypervisor active and guest in kernel mode   PCID 0
+ * - hypervisor active and guest in user mode     PCID 1
+ * - guest active and in kernel mode              PCID 2
+ * - guest active and in user mode                PCID 3
+ *
+ * Without XPTI only 2 values are used:
+ * - guest in kernel mode                         PCID 0
+ * - guest in user mode                           PCID 1
+ */
+
+#define PCID_PV_PRIV      0x0000    /* Used for other domains, too. */
+#define PCID_PV_USER      0x0001
+#define PCID_PV_XPTI      0x0002    /* To be ORed to above values. */
+
+/*
+ * Return additional PCID specific cr3 bits.
+ *
+ * Note that X86_CR3_NOFLUSH will not be readable in cr3. Anyone consuming
+ * v->arch.cr3 should mask away X86_CR3_NOFLUSH and X86_CR3_PCIDMASK in case
+ * the value is used to address the root page table.
+ */
+#define get_pcid_bits(v, is_xpti)                                       \
+    (X86_CR3_NOFLUSH | ((is_xpti) ? PCID_PV_XPTI : 0) |                 \
+     (((v)->arch.flags & TF_kernel_mode) ? PCID_PV_PRIV : PCID_PV_USER))
+
 struct arch_domain
 {
     struct page_info *perdomain_l3_pg;
@@ -505,7 +536,8 @@ unsigned long pv_guest_cr4_to_real_cr4(c
 
 #define real_cr4_to_pv_guest_cr4(c)                         \
     ((c) & ~(X86_CR4_PGE | X86_CR4_PSE | X86_CR4_TSD |      \
-             X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE))
+             X86_CR4_OSXSAVE | X86_CR4_SMEP |               \
+             X86_CR4_FSGSBASE | X86_CR4_PCIDE))
 
 void domain_cpuid(struct domain *d,
                   unsigned int  input,
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -340,6 +340,9 @@ static inline unsigned long read_cr4(voi
 
 static inline void write_cr4(unsigned long val)
 {
+    /* No global pages in case of PCIDs enabled! */
+    ASSERT(!(val & X86_CR4_PGE) || !(val & X86_CR4_PCIDE));
+
     this_cpu(cr4) = val;
     asm volatile ( "mov %0,%%cr4" : : "r" (val) );
 }
