sys: Fix PVALIDATE carry flag detection

The assembler code for PVALIDATE performs an XOR immediately after the PVALIDATE instruction, which clears the carry-flag, causing the carry-flag result of the PVALIDATE instruction to be lost. Move the XOR before the PVALIDATE instruction and switch to using the R8 register since the RCX register is used as input to PVALIDATE Signed-off-by: Tom Lendacky <[email protected]>
AMDESE · Jan 10, 2024 · 4b2cab1 · 4b2cab1
1 parent 1801cf2
commit 4b2cab1
Showing 1 changed file with 4 additions and 4 deletions.
diff --git a/src/cpu/sys.rs b/src/cpu/sys.rs
@@ -83,13 +83,13 @@ pub fn pvalidate(va: u64, page_size: u32, validation: u32) -> u32 {
     let mut carry: u32;
 
     unsafe {
-        asm!(".byte 0xf2,0x0f,0x01,0xff",
-             "xor rcx, rcx",
+        asm!("xor r8, r8",
+             ".byte 0xf2,0x0f,0x01,0xff",
              "jnc 1f",
-             "inc rcx",
+             "inc r8",
              "1:",
              in("rax") va, in("rcx") page_size, in("rdx") validation,
-             lateout("rax") ret, lateout("rcx") carry,
+             lateout("rax") ret, lateout("r8") carry,
              options(nostack));
     }