Re: [RFC][PATCH 2/3] x86/uaccess: Implement unsafe_try_cmpxchg_user()
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-12-21 11:18:16
Also in:
linux-mm, lkml
On Mon, Dec 20, 2021 at 05:30:05PM +0000, Sean Christopherson wrote:
On Tue, Dec 14, 2021, Peter Zijlstra wrote:quoted
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.
Sure, no problem. I currently still need to audit parts of mm/ and do the smp-wake-idle bits before I repost -- that and take a xmas break ofcourse :-) So it'll be a while before I repost this.