x86/sev: Make the VMPL0 checking more straight forward

Currently, the enforce_vmpl0() function uses a set argument when modifying
the VMPL1 permissions used to test for VMPL0. If the guest is not running
at VMPL0, the guest self-terminates.

The function is just a wrapper for a fixed RMPADJUST function. Eliminate
the function and perform the RMPADJUST directly.

No functional change.

Signed-off-by: Tom Lendacky <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Link: https://lore.kernel.org/r/ed01ddf04bfb475596b24b634fd26cffaa85173a.1713974291.git.thomas.lendacky@amd.com

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 5ad0ff4664f14dad019925ef28b0532f770cdf55..0457a9d7e5150f17a7f4bb24783bed9ac22072f1 100644 (file)
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -335,26 +335,6 @@ finish:
                sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
 }
 
-static void enforce_vmpl0(void)
-{
-       u64 attrs;
-       int err;
-
-       /*
-        * RMPADJUST modifies RMP permissions of a lesser-privileged (numerically
-        * higher) privilege level. Here, clear the VMPL1 permission mask of the
-        * GHCB page. If the guest is not running at VMPL0, this will fail.
-        *
-        * If the guest is running at VMPL0, it will succeed. Even if that operation
-        * modifies permission bits, it is still ok to do so currently because Linux
-        * SNP guests are supported only on VMPL0 so VMPL1 or higher permission masks
-        * changing is a don't-care.
-        */
-       attrs = 1;
-       if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, attrs))
-               sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
-}
-
 /*
  * SNP_FEATURES_IMPL_REQ is the mask of SNP features that will need
  * guest side implementation for proper functioning of the guest. If any
@@ -588,7 +568,20 @@ void sev_enable(struct boot_params *bp)
                if (!(get_hv_features() & GHCB_HV_FT_SNP))
                        sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
 
-               enforce_vmpl0();
+               /*
+                * Enforce running at VMPL0.
+                *
+                * RMPADJUST modifies RMP permissions of a lesser-privileged (numerically
+                * higher) privilege level. Here, clear the VMPL1 permission mask of the
+                * GHCB page. If the guest is not running at VMPL0, this will fail.
+                *
+                * If the guest is running at VMPL0, it will succeed. Even if that operation
+                * modifies permission bits, it is still ok to do so currently because Linux
+                * SNP guests running at VMPL0 only run at VMPL0, so VMPL1 or higher
+                * permission mask changes are a don't-care.
+                */
+               if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1))
+                       sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
        }
 
        if (snp && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))