On 20/04/2020 14:47, Roger Pau Monné wrote: > On Fri, Apr 17, 2020 at 04:50:02PM +0100, Andrew Cooper wrote: >> 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 or architectural corner cases, such as counting as supervisor > ^ of
Already fixed (I spotted it 30s after posting). >> 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.coop...@citrix.com> >> --- >> CC: Jan Beulich <jbeul...@suse.com> >> CC: Wei Liu <w...@xen.org> >> CC: Roger Pau Monné <roger....@citrix.com> >> >> There is a series I can't quite post yet which wants to conditionally turn >> opt_pv32 off, which is why I've put it straight in in an int8_t form rather > s/in in/in/ "in in" is legitimate in some cases, despite it looking awkard. In this case, the structure is "straight in", separate from "in an int8_t form". If this sentence were for inclusion in the commit message, I'd have probably spent more effort trying to phrase it differently. > >> than a straight boolean form. >> --- >> docs/misc/xen-command-line.pandoc | 12 +++++++++++- >> xen/arch/x86/Kconfig | 16 ++++++++++++++++ >> xen/arch/x86/pv/domain.c | 35 +++++++++++++++++++++++++++++++++++ >> xen/arch/x86/setup.c | 9 +++++++-- >> xen/include/asm-x86/pv/domain.h | 6 ++++++ >> 5 files changed, 75 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 8149362bde..4c52197de3 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 70fae43965..47a0db082f 100644 >> --- a/xen/arch/x86/pv/domain.c >> +++ b/xen/arch/x86/pv/domain.c >> @@ -16,6 +16,39 @@ >> #include <asm/pv/domain.h> >> #include <asm/shadow.h> >> >> +#ifdef CONFIG_PV32 >> +int8_t __read_mostly opt_pv32 = -1; >> +#endif >> + >> +static int parse_pv(const char *s) > __init > > With that: > > Reviewed-by: Roger Pau Monné <roger....@citrix.com> Thanks, ~Andrew
