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xen.21116
60afe618-x86-TSX-deprecate-vpmu=rtm-abort.patch
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File 60afe618-x86-TSX-deprecate-vpmu=rtm-abort.patch of Package xen.21116
# Commit 9fdcf851689cb2a9501d3947cb5d767d9c7797e8 # Date 2021-05-27 19:34:00 +0100 # Author Andrew Cooper <andrew.cooper3@citrix.com> # Committer Andrew Cooper <andrew.cooper3@citrix.com> x86/tsx: Deprecate vpmu=rtm-abort and use tsx=<bool> instead This reuses the rtm_disable infrastructure, so CPUID derivation works properly when TSX is disabled in favour of working PCR3. vpmu= is not a supported feature, and having this functionality under tsx= centralises all TSX handling. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Acked-by: Jan Beulich <jbeulich@suse.com> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> --- a/docs/misc/xen-command-line.pandoc +++ b/docs/misc/xen-command-line.pandoc @@ -2231,14 +2231,21 @@ pages) must also be specified via the tb Controls for the use of Transactional Synchronization eXtensions. -On Intel parts released in Q3 2019 (with updated microcode), and future parts, -a control has been introduced which allows TSX to be turned off. +Several microcode updates are relevant: -On systems with the ability to turn TSX off, this boolean offers system wide -control of whether TSX is enabled or disabled. + * March 2019, fixing the TSX memory ordering errata on all TSX-enabled CPUs + to date. Introduced MSR_TSX_FORCE_ABORT on SKL/SKX/KBL/WHL/CFL parts. The + errata workaround uses Performance Counter 3, so the user can select + between working TSX and working perfcounters. + + * November 2019, fixing the TSX Async Abort speculative vulnerability. + Introduced MSR_TSX_CTRL on all TSX-enabled MDS_NO parts to date, + CLX/WHL-R/CFL-R, with the controls becoming architectural moving forward + and formally retiring HLE from the architecture. The user can disable TSX + to mitigate TAA, and elect to hide the HLE/RTM CPUID bits. -On parts vulnerable to CVE-2019-11135 / TSX Asynchronous Abort, the following -logic applies: +On systems with the ability to configure TSX, this boolean offers system wide +control of whether TSX is enabled or disabled. * An explicit `tsx=` choice is honoured, even if it is `true` and would result in a vulnerable system. @@ -2246,10 +2253,14 @@ logic applies: * When no explicit `tsx=` choice is given, parts vulnerable to TAA will be mitigated by disabling TSX, as this is the lowest overhead option. - * If the use of TSX is important, the more expensive TAA mitigations can be + If the use of TSX is important, the more expensive TAA mitigations can be opted in to with `smt=0 spec-ctrl=md-clear`, at which point TSX will remain active by default. + * When no explicit `tsx=` option is given, parts susceptible to the memory + ordering errata default to `true` to enable working TSX. Alternatively, + selecting `tsx=0` will disable TSX and restore PCR3 to a working state. + ### ucode > `= List of [ <integer> | scan=<bool>, nmi=<bool> ]` @@ -2386,20 +2397,7 @@ provide access to a wealth of low level * The `arch` option allows access to the pre-defined architectural events. -* The `rtm-abort` boolean controls a trade-off between working Restricted - Transactional Memory, and working performance counters. - - All processors released to date (Q1 2019) supporting Transactional Memory - Extensions suffer an erratum which has been addressed in microcode. - - Processors based on the Skylake microarchitecture with up-to-date - microcode internally use performance counter 3 to work around the erratum. - A consequence is that the counter gets reprogrammed whenever an `XBEGIN` - instruction is executed. - - An alternative mode exists where PCR3 behaves as before, at the cost of - `XBEGIN` unconditionally aborting. Enabling `rtm-abort` mode will - activate this alternative mode. +* The `rtm-abort` boolean has been superseded. Use `tsx=0` instead. *Warning:* As the virtualisation is not 100% safe, don't use the vpmu flag on --- a/xen/arch/x86/cpu/intel.c +++ b/xen/arch/x86/cpu/intel.c @@ -356,9 +356,6 @@ static void Intel_errata_workarounds(str (c->x86_model == 29 || c->x86_model == 46 || c->x86_model == 47)) __set_bit(X86_FEATURE_CLFLUSH_MONITOR, c->x86_capability); - if (cpu_has_tsx_force_abort && opt_rtm_abort) - wrmsrl(MSR_TSX_FORCE_ABORT, TSX_FORCE_ABORT_RTM); - probe_c3_errata(c); } --- a/xen/arch/x86/cpu/vpmu.c +++ b/xen/arch/x86/cpu/vpmu.c @@ -47,7 +47,6 @@ CHECK_pmu_params; static unsigned int __read_mostly opt_vpmu_enabled; unsigned int __read_mostly vpmu_mode = XENPMU_MODE_OFF; unsigned int __read_mostly vpmu_features = 0; -bool __read_mostly opt_rtm_abort; static DEFINE_SPINLOCK(vpmu_lock); static unsigned vpmu_count; @@ -77,7 +76,8 @@ static int __init parse_vpmu_params(cons else if ( !cmdline_strcmp(s, "arch") ) vpmu_features |= XENPMU_FEATURE_ARCH_ONLY; else if ( (val = parse_boolean("rtm-abort", s, ss)) >= 0 ) - opt_rtm_abort = val; + printk(XENLOG_WARNING + "'rtm-abort=<bool>' superseded. Use 'tsx=<bool>' instead\n"); else rc = -EINVAL; --- a/xen/arch/x86/tsx.c +++ b/xen/arch/x86/tsx.c @@ -6,7 +6,9 @@ * Valid values: * 1 => Explicit tsx=1 * 0 => Explicit tsx=0 - * -1 => Default, implicit tsx=1, may change to 0 to mitigate TAA + * -1 => Default, altered to 0/1 (if unspecified) by: + * - TAA heuristics/settings for speculative safety + * - "TSX vs PCR3" select for TSX memory ordering safety * -3 => Implicit tsx=1 (feed-through from spec-ctrl=0) * * This is arranged such that the bottom bit encodes whether TSX is actually @@ -50,6 +52,26 @@ void tsx_init(void) cpu_has_tsx_ctrl = !!(caps & ARCH_CAPS_TSX_CTRL); + if ( cpu_has_tsx_force_abort ) + { + /* + * On an early TSX-enable Skylake part subject to the memory + * ordering erratum, with at least the March 2019 microcode. + */ + + /* + * If no explicit tsx= option is provided, pick a default. + * + * This deliberately overrides the implicit opt_tsx=-3 from + * `spec-ctrl=0` because: + * - parse_spec_ctrl() ran before any CPU details where know. + * - We now know we're running on a CPU not affected by TAA (as + * TSX_FORCE_ABORT is enumerated). + */ + if ( opt_tsx < 0 ) + opt_tsx = 1; + } + /* * The TSX features (HLE/RTM) are handled specially. They both * enumerate features but, on certain parts, have mechanisms to be @@ -75,6 +97,12 @@ void tsx_init(void) } } + /* + * Note: MSR_TSX_CTRL is enumerated on TSX-enabled MDS_NO and later parts. + * MSR_TSX_FORCE_ABORT is enumerated on TSX-enabled pre-MDS_NO Skylake + * parts only. The two features are on a disjoint set of CPUs, and not + * offered to guests by hypervisors. + */ if ( cpu_has_tsx_ctrl ) { uint32_t hi, lo; @@ -90,9 +118,28 @@ void tsx_init(void) wrmsr(MSR_TSX_CTRL, lo, hi); } + else if ( cpu_has_tsx_force_abort ) + { + /* + * On an early TSX-enable Skylake part subject to the memory ordering + * erratum, with at least the March 2019 microcode. + */ + uint32_t hi, lo; + + rdmsr(MSR_TSX_FORCE_ABORT, lo, hi); + + /* Check bottom bit only. Higher bits are various sentinels. */ + rtm_disabled = !(opt_tsx & 1); + + lo &= ~TSX_FORCE_ABORT_RTM; + if ( rtm_disabled ) + lo |= TSX_FORCE_ABORT_RTM; + + wrmsr(MSR_TSX_FORCE_ABORT, lo, hi); + } else if ( opt_tsx >= 0 ) printk_once(XENLOG_WARNING - "MSR_TSX_CTRL not available - Ignoring tsx= setting\n"); + "TSX controls not available - Ignoring tsx= setting\n"); } /* --- a/xen/include/asm-x86/vpmu.h +++ b/xen/include/asm-x86/vpmu.h @@ -126,7 +126,6 @@ static inline int vpmu_do_rdmsr(unsigned extern unsigned int vpmu_mode; extern unsigned int vpmu_features; -extern bool opt_rtm_abort; /* Context switch */ static inline void vpmu_switch_from(struct vcpu *prev)
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