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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging] x86/pv: Options to disable and/or compile out 32bit PV support
commit 68d757df8dd23b88bebfb6a56c9f51df59de969f
Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Apr 17 12:39:40 2020 +0100
Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Apr 29 21:13:00 2020 +0100
x86/pv: Options to disable and/or compile out 32bit PV support
This is the start of some performance and security-hardening improvements,
based on the fact that 32bit PV guests are few and far between these days.
Ring1 is full of architectural corner cases, such as counting as supervisor
from a paging point of view. This accounts for a substantial performance
hit
on processors from the last 8 years (adjusting SMEP/SMAP on every privilege
transition), and the gap is only going to get bigger with new hardware
features.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Wei Liu <wl@xxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
docs/misc/xen-command-line.pandoc | 12 +++++++++++-
xen/arch/x86/Kconfig | 16 ++++++++++++++++
xen/arch/x86/pv/domain.c | 34 ++++++++++++++++++++++++++++++++++
xen/arch/x86/setup.c | 9 +++++++--
xen/include/asm-x86/pv/domain.h | 6 ++++++
xen/include/xen/param.h | 9 +++++++++
6 files changed, 83 insertions(+), 3 deletions(-)
diff --git a/docs/misc/xen-command-line.pandoc
b/docs/misc/xen-command-line.pandoc
index acd0b3d994..ee12b0f53f 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1694,7 +1694,17 @@ The following resources are available:
CDP, one COS will corespond two CBMs other than one with CAT, due to the
sum of CBMs is fixed, that means actual `cos_max` in use will automatically
reduce to half when CDP is enabled.
-
+
+### pv
+ = List of [ 32=<bool> ]
+
+ Applicability: x86
+
+Controls for aspects of PV guest support.
+
+* The `32` boolean controls whether 32bit PV guests can be created. It
+ defaults to `true`, and is ignored when `CONFIG_PV32` is compiled out.
+
### pv-linear-pt (x86)
> `= <boolean>`
diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index a69be983d6..96432f1f69 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -49,6 +49,22 @@ config PV
If unsure, say Y.
+config PV32
+ bool "Support for 32bit PV guests"
+ depends on PV
+ default y
+ ---help---
+ The 32bit PV ABI uses Ring1, an area of the x86 architecture which
+ was deprecated and mostly removed in the AMD64 spec. As a result,
+ it occasionally conflicts with newer x86 hardware features, causing
+ overheads for Xen to maintain backwards compatibility.
+
+ People may wish to disable 32bit PV guests for attack surface
+ reduction, or performance reasons. Backwards compatibility can be
+ provided via the PV Shim mechanism.
+
+ If unsure, say Y.
+
config PV_LINEAR_PT
bool "Support for PV linear pagetables"
depends on PV
diff --git a/xen/arch/x86/pv/domain.c b/xen/arch/x86/pv/domain.c
index 43da5c179f..3579dc063e 100644
--- a/xen/arch/x86/pv/domain.c
+++ b/xen/arch/x86/pv/domain.c
@@ -16,6 +16,38 @@
#include <asm/pv/domain.h>
#include <asm/shadow.h>
+#ifdef CONFIG_PV32
+int8_t __read_mostly opt_pv32 = -1;
+#endif
+
+static __init int parse_pv(const char *s)
+{
+ const char *ss;
+ int val, rc = 0;
+
+ do {
+ ss = strchr(s, ',');
+ if ( !ss )
+ ss = strchr(s, '\0');
+
+ if ( (val = parse_boolean("32", s, ss)) >= 0 )
+ {
+#ifdef CONFIG_PV32
+ opt_pv32 = val;
+#else
+ no_config_param("PV32", "pv", s, ss);
+#endif
+ }
+ else
+ rc = -EINVAL;
+
+ s = ss + 1;
+ } while ( *ss );
+
+ return rc;
+}
+custom_param("pv", parse_pv);
+
static __read_mostly enum {
PCID_OFF,
PCID_ALL,
@@ -174,6 +206,8 @@ int switch_compat(struct domain *d)
BUILD_BUG_ON(offsetof(struct shared_info, vcpu_info) != 0);
+ if ( !opt_pv32 )
+ return -EOPNOTSUPP;
if ( is_hvm_domain(d) || domain_tot_pages(d) != 0 )
return -EACCES;
if ( is_pv_32bit_domain(d) )
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index eb56d78c2f..9e9576344c 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -53,6 +53,7 @@
#include <asm/spec_ctrl.h>
#include <asm/guest.h>
#include <asm/microcode.h>
+#include <asm/pv/domain.h>
/* opt_nosmp: If true, secondary processors are ignored. */
static bool __initdata opt_nosmp;
@@ -1870,8 +1871,12 @@ void arch_get_xen_caps(xen_capabilities_info_t *info)
{
snprintf(s, sizeof(s), "xen-%d.%d-x86_64 ", major, minor);
safe_strcat(*info, s);
- snprintf(s, sizeof(s), "xen-%d.%d-x86_32p ", major, minor);
- safe_strcat(*info, s);
+
+ if ( opt_pv32 )
+ {
+ snprintf(s, sizeof(s), "xen-%d.%d-x86_32p ", major, minor);
+ safe_strcat(*info, s);
+ }
}
if ( hvm_enabled )
{
diff --git a/xen/include/asm-x86/pv/domain.h b/xen/include/asm-x86/pv/domain.h
index 7a69bfb303..df9716ff26 100644
--- a/xen/include/asm-x86/pv/domain.h
+++ b/xen/include/asm-x86/pv/domain.h
@@ -23,6 +23,12 @@
#include <xen/sched.h>
+#ifdef CONFIG_PV32
+extern int8_t opt_pv32;
+#else
+# define opt_pv32 false
+#endif
+
/*
* PCID values for the address spaces of 64-bit pv domains:
*
diff --git a/xen/include/xen/param.h b/xen/include/xen/param.h
index d4578cd27f..a1dc3ba8f0 100644
--- a/xen/include/xen/param.h
+++ b/xen/include/xen/param.h
@@ -127,4 +127,13 @@ extern const struct kernel_param __param_start[],
__param_end[];
string_param(_name, _var); \
string_runtime_only_param(_name, _var)
+static inline void no_config_param(const char *cfg, const char *param,
+ const char *s, const char *e)
+{
+ int len = e ? ({ ASSERT(e >= s); e - s; }) : strlen(s);
+
+ printk(XENLOG_INFO "CONFIG_%s disabled - ignoring '%s=%*s' setting\n",
+ cfg, param, len, s);
+}
+
#endif /* _XEN_PARAM_H */
--
generated by git-patchbot for /home/xen/git/xen.git#staging
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