From: Sean Christopherson <seanjc@google.com>
To: kernel test robot <lkp@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
llvm@lists.linux.dev, kbuild-all@lists.01.org,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org
Subject: Re: [PATCH 3/5] KVM: x86: Use __try_cmpxchg_user() to update guest PTE A/D bits
Date: Tue, 1 Feb 2022 19:44:47 +0000 [thread overview]
Message-ID: <YfmNr8OjOWvsQBKx@google.com> (raw)
In-Reply-To: <202202011400.EaZmWZ48-lkp@intel.com>
On Tue, Feb 01, 2022, kernel test robot wrote:
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
> In file included from arch/x86/kvm/mmu/mmu.c:4246:
> >> arch/x86/kvm/mmu/paging_tmpl.h:244:9: error: invalid output size for constraint '+a'
> ret = __try_cmpxchg_user(ptep_user, &orig_pte, pte, fault);
> ^
> arch/x86/include/asm/uaccess.h:629:11: note: expanded from macro '__try_cmpxchg_user'
> __ret = !unsafe_try_cmpxchg_user(_ptr, _oldp, _nval, _label); \
> ^
> arch/x86/include/asm/uaccess.h:606:18: note: expanded from macro 'unsafe_try_cmpxchg_user'
> case 1: __ret = __try_cmpxchg_user_asm("b", "q", \
> ^
> arch/x86/include/asm/uaccess.h:467:22: note: expanded from macro '__try_cmpxchg_user_asm'
> [old] "+a" (__old) \
#$*&(#$ clang.
clang isn't smart enough to avoid compiling the impossible conditions it will
throw away in the end, i.e. it compiles all cases given:
switch (8) {
case 1:
case 2:
case 4:
case 8:
}
I can fudge around that by casting the pointer, which I don't think can go sideways
if the pointer value is a signed type?
@@ -604,15 +602,15 @@ extern void __try_cmpxchg_user_wrong_size(void);
bool __ret; \
switch (sizeof(*(_ptr))) { \
case 1: __ret = __try_cmpxchg_user_asm("b", "q", \
- (_ptr), (_oldp), \
+ (u8 *)(_ptr), (_oldp), \
(_nval), _label); \
break; \
case 2: __ret = __try_cmpxchg_user_asm("w", "r", \
- (_ptr), (_oldp), \
+ (u16 *)(_ptr), (_oldp), \
(_nval), _label); \
break; \
case 4: __ret = __try_cmpxchg_user_asm("l", "r", \
- (_ptr), (_oldp), \
+ (u32 *)(_ptr), (_oldp), \
(_nval), _label); \
break; \
case 8: __ret = __try_cmpxchg64_user_asm((_ptr), (_oldp), \
clang also lacks the intelligence to realize that it can/should use a single
register for encoding the memory operand and consumes both ESI and EDI, leaving
no register for the __err "+r" param in __try_cmpxchg64_user_asm(). That can be
avoided by open coding CC_SET and using a single output register for both the
result and the -EFAULT error path.
next prev parent reply other threads:[~2022-02-01 19:44 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-01 1:08 [PATCH 0/5] x86: uaccess CMPXCHG + KVM bug fixes Sean Christopherson
2022-02-01 1:08 ` [PATCH 1/5] Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug Sean Christopherson
2022-02-01 20:16 ` Nick Desaulniers
2022-02-01 20:56 ` Sean Christopherson
2022-02-01 21:15 ` Nick Desaulniers
2022-02-01 1:08 ` [PATCH 2/5] x86/uaccess: Implement macros for CMPXCHG on user addresses Sean Christopherson
2022-02-01 1:08 ` [PATCH 3/5] KVM: x86: Use __try_cmpxchg_user() to update guest PTE A/D bits Sean Christopherson
2022-02-01 7:01 ` kernel test robot
2022-02-01 19:44 ` Sean Christopherson [this message]
2022-02-01 19:53 ` Nick Desaulniers
2022-02-01 13:25 ` kernel test robot
2022-02-01 1:08 ` [PATCH 4/5] KVM: x86: Use __try_cmpxchg_user() to emulate atomic accesses Sean Christopherson
2022-02-01 9:25 ` kernel test robot
2022-02-01 1:08 ` [PATCH 5/5] KVM: x86: Bail to userspace if emulation of atomic user access faults Sean Christopherson
2022-02-01 17:09 ` [PATCH 0/5] x86: uaccess CMPXCHG + KVM bug fixes Tadeusz Struk
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