Re: [RFC][PATCH 2/3] x86/uaccess: Implement unsafe_try_cmpxchg_user()
From: Sean Christopherson <seanjc@google.com>
Date: 2021-12-20 17:30:13
Also in:
linux-api, lkml
On Tue, Dec 14, 2021, Peter Zijlstra wrote:
quoted hunk ↗ jump to hunk
Do try_cmpxchg() loops on userspace addresses. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> ---@@ -501,6 +543,21 @@ do { \ } while (0) #endif // CONFIG_CC_HAS_ASM_GOTO_OUTPUT +extern void __try_cmpxchg_user_wrong_size(void); + +#define unsafe_try_cmpxchg_user(_ptr, _oldp, _nval, _label) ({ \ + __typeof__(*(_ptr)) __ret; \ + switch (sizeof(__ret)) { \ + case 4: __ret = __try_cmpxchg_user_asm("l", (_ptr), (_oldp), \ + (_nval), _label); \ + break; \ + case 8: __ret = __try_cmpxchg_user_asm("q", (_ptr), (_oldp), \ + (_nval), _label); \ + break; \
Can we add support for 1-byte and 2-byte cmpxchg, and for using cmpxchg8b to handle 8-byte operations in 32-bit mode? Support for all the flavors (except 16-byte) would allow KVM to use this in an emulator path that currently kmaps the target. I'd be more than happy to help test the result. Thanks!
+ default: __try_cmpxchg_user_wrong_size(); \ + } \ + __ret; }) + /* * We want the unsafe accessors to always be inlined and use * the error labels - thus the macro games.