x86: kvm: avoid constant-conversion warning

clang finds a contruct suspicious that converts an unsigned
character to a signed integer and back, causing an overflow:

arch/x86/kvm/mmu.c:4605:39: error: implicit conversion from 'int' to 'u8' (aka 'unsigned char') changes value from -205 to 51 [-Werror,-Wconstant-conversion]
                u8 wf = (pfec & PFERR_WRITE_MASK) ? ~w : 0;
                   ~~                               ^~
arch/x86/kvm/mmu.c:4607:38: error: implicit conversion from 'int' to 'u8' (aka 'unsigned char') changes value from -241 to 15 [-Werror,-Wconstant-conversion]
                u8 uf = (pfec & PFERR_USER_MASK) ? ~u : 0;
                   ~~                              ^~
arch/x86/kvm/mmu.c:4609:39: error: implicit conversion from 'int' to 'u8' (aka 'unsigned char') changes value from -171 to 85 [-Werror,-Wconstant-conversion]
                u8 ff = (pfec & PFERR_FETCH_MASK) ? ~x : 0;
                   ~~                               ^~

Add an explicit cast to tell clang that everything works as
intended here.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://github.com/ClangBuiltLinux/linux/issues/95
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9a5814d..8f72526 100644 (file)
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4597,11 +4597,11 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu,
                 */
 
                /* Faults from writes to non-writable pages */
-               u8 wf = (pfec & PFERR_WRITE_MASK) ? ~w : 0;
+               u8 wf = (pfec & PFERR_WRITE_MASK) ? (u8)~w : 0;
                /* Faults from user mode accesses to supervisor pages */
-               u8 uf = (pfec & PFERR_USER_MASK) ? ~u : 0;
+               u8 uf = (pfec & PFERR_USER_MASK) ? (u8)~u : 0;
                /* Faults from fetches of non-executable pages*/
-               u8 ff = (pfec & PFERR_FETCH_MASK) ? ~x : 0;
+               u8 ff = (pfec & PFERR_FETCH_MASK) ? (u8)~x : 0;
                /* Faults from kernel mode fetches of user pages */
                u8 smepf = 0;
                /* Faults from kernel mode accesses of user pages */