17 research outputs found
Isla: Integrating full-scale ISA semantics and axiomatic concurrency models (extended version)
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Relaxed virtual memory in Armv8-A
Virtual memory is an essential mechanism for enforcing security boundaries, but its relaxed-memory concurrency semantics has not previously been investigated in detail.
The concurrent systems code managing virtual memory has been left on an entirely informal basis, and OS and hypervisor verification has had to make major simplifying assumptions.
We explore the design space for relaxed virtual memory semantics in the Armv8-A architecture, to support future system-software verification. We identify many design questions, in discussion with Arm; develop a test suite, including use cases from the pKVM production hypervisor under development by Google; delimit the design space with axiomatic-style concurrency models; prove that under simple stable configurations our architectural model collapses to previous "user" models; develop tooling to compute allowed behaviours in the model integrated with the full Armv8-A ISA semantics; and develop a hardware test harness.
This lays out some of the main issues in relaxed virtual memory, bringing these security-critical systems phenomena into the domain of programming-language semantics and verification, with foundational architecture semantics, for the first time.This work was partially funded by an Arm/EPSRC iCASE PhD studentship (Simner), Arm Limited, Google, ERC Advanced Grant (AdG) 789108 ELVER, and the UK Government Industrial Strategy Challenge Fund (ISCF) under the Digital Security by Design (DSbD) Programme, to deliver a DSbDtech enabled digital platform (grant 105694)
Concern for Others in the First Year of Life: Theory, Evidence, and Avenues for Research
A different outlook on time: Visual and auditory month names elicit different mental vantage points for a time-space synaesthete
Antimicrobial Resistance in Urinary Tract Pathogens in Canada from 2007 to 2009: CANWARD Surveillance Study ▿
From January 2007 to December 2009, an annual Canadian national surveillance study (CANWARD) tested 2,943 urinary culture pathogens for antimicrobial susceptibilities according to Clinical and Laboratory Standards Institute guidelines. The most frequently isolated urinary pathogens were as follows (number of isolates, percentage of all isolates): Escherichia coli (1,581, 54%), enterococci (410, 14%), Klebsiella pneumoniae (274, 9%), Proteus mirabilis (122, 4%), Pseudomonas aeruginosa (100, 3%), and Staphylococcus aureus (80, 3%). The rates of susceptibility to trimethoprim-sulfamethoxazole (SXT) were 78, 86, 84, and 93%, respectively, for E. coli, K. pneumoniae, P. mirabilis, and S. aureus. The rates of susceptibility to nitrofurantoin were 96, 97, 33, and 100%, respectively, for E. coli, enterococci, K. pneumoniae, and S. aureus. The rates of susceptibility to ciprofloxacin were 81, 40, 86, 81, 66, and 41%, respectively, for E. coli, enterococci, K. pneumoniae, P. mirabilis, P. aeruginosa, and S. aureus. Statistical analysis of resistance rates (resistant plus intermediate isolates) by year for E. coli over the 3-year study period demonstrated that increased resistance rates occurred only for amoxicillin-clavulanate (from 1.8 to 6.6%; P < 0.001) and for SXT (from 18.6 to 24.3%; P = 0.02). For isolates of E. coli, in a multivariate logistic regression model, hospital location was independently associated with resistance to ciprofloxacin (P = 0.026) with higher rates of resistance observed in inpatient areas (medical, surgical, and intensive care unit wards). Increased age was also associated with resistance to ciprofloxacin (P < 0.001) and with resistance to two or more commonly prescribed oral agents (amoxicillin-clavulanate, ciprofloxacin, nitrofurantoin, and SXT) (P = 0.005). We conclude that frequently prescribed empirical agents for urinary tract infections, such as SXT and ciprofloxacin, demonstrate lowered in vitro susceptibilities when tested against recent clinical isolates