Messages in this thread |  | | Subject | Re: [PATCH v2 3/6] kvm: x86: Emulate split-lock access as a write | From | Xiaoyao Li <> | Date | Tue, 4 Feb 2020 10:55:40 +0800 |
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On 2/4/2020 4:54 AM, Sean Christopherson wrote: > On Mon, Feb 03, 2020 at 11:16:05PM +0800, Xiaoyao Li wrote: >> If split lock detect is enabled (warn/fatal), #AC handler calls die() >> when split lock happens in kernel. >> >> A sane guest should never tigger emulation on a split-lock access, but >> it cannot prevent malicous guest from doing this. So just emulating the >> access as a write if it's a split-lock access to avoid malicous guest >> polluting the kernel log. >> >> More detail analysis can be found: >> https://lkml.kernel.org/r/20200131200134.GD18946@linux.intel.com >> >> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com> >> --- >> arch/x86/kvm/x86.c | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 2d3be7f3ad67..821b7404c0fd 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -5847,6 +5847,13 @@ static int emulator_write_emulated(struct x86_emulate_ctxt *ctxt, >> (cmpxchg64((u64 *)(ptr), *(u64 *)(old), *(u64 *)(new)) == *(u64 *)(old)) >> #endif >> >> +static inline bool across_cache_line_access(gpa_t gpa, unsigned int bytes) > > s/across/split so as not to introduce another name. > >> +{ >> + unsigned int cache_line_size = cache_line_size(); >> + >> + return (gpa & (cache_line_size - 1)) + bytes > cache_line_size; > > I'd prefer to use the same logic as the page-split to avoid having to > reason about the correctness of two different algorithms. > >> +} >> + >> static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, >> unsigned long addr, >> const void *old, >> @@ -5873,6 +5880,10 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, >> if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK)) >> goto emul_write; >> >> + if (get_split_lock_detect_state() != sld_off && >> + across_cache_line_access(gpa, bytes)) >> + goto emul_write; > > As an alternative to the above, the page/line splits can be handled in a > single check, e.g. > > page_line_mask = PAGE_MASK; > if (is_split_lock_detect_enabled()) > page_line_mask = cache_line_size() - 1; > if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask)) > goto emul_write;
It's better, will use your suggestion. Thanks!
>> + >> if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map)) >> goto emul_write; >> >> -- >> 2.23.0 >>
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