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x86/bugs: Restructure MMIO mitigation

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Restructure MMIO mitigation to use select/update/apply functions to
create consistent vulnerability handling.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/20250418161721.1855190-4-david.kaplan@amd.com
This commit is contained in:
David Kaplan
2025-04-18 11:17:08 -05:00
committed by Borislav Petkov (AMD)
parent bdd7fce7a8
commit 4a5a04e61d
1 changed files with 50 additions and 24 deletions
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74
arch/x86/kernel/cpu/bugs.c
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@@ -68,6 +68,8 @@ static void __init taa_select_mitigation(void);
static void __init taa_update_mitigation(void);
static void __init taa_apply_mitigation(void);
static void __init mmio_select_mitigation(void);
static void __init mmio_update_mitigation(void);
static void __init mmio_apply_mitigation(void);
static void __init srbds_select_mitigation(void);
static void __init l1d_flush_select_mitigation(void);
static void __init srso_select_mitigation(void);
@@ -197,6 +199,7 @@ void __init cpu_select_mitigations(void)
l1tf_select_mitigation();
mds_select_mitigation();
taa_select_mitigation();
mmio_select_mitigation();
md_clear_select_mitigation();
srbds_select_mitigation();
l1d_flush_select_mitigation();
@@ -214,9 +217,11 @@ void __init cpu_select_mitigations(void)
*/
mds_update_mitigation();
taa_update_mitigation();
mmio_update_mitigation();
mds_apply_mitigation();
taa_apply_mitigation();
mmio_apply_mitigation();
}
/*
@@ -520,25 +525,62 @@ static void __init mmio_select_mitigation(void)
return;
}
/* Microcode will be checked in mmio_update_mitigation(). */
if (mmio_mitigation == MMIO_MITIGATION_AUTO)
mmio_mitigation = MMIO_MITIGATION_VERW;
if (mmio_mitigation == MMIO_MITIGATION_OFF)
return;
/*
* Enable CPU buffer clear mitigation for host and VMM, if also affected
* by MDS or TAA. Otherwise, enable mitigation for VMM only.
* by MDS or TAA.
*/
if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
boot_cpu_has(X86_FEATURE_RTM)))
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
if (boot_cpu_has_bug(X86_BUG_MDS) || taa_vulnerable())
verw_clear_cpu_buf_mitigation_selected = true;
}
static void __init mmio_update_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) || cpu_mitigations_off())
return;
if (verw_clear_cpu_buf_mitigation_selected)
mmio_mitigation = MMIO_MITIGATION_VERW;
if (mmio_mitigation == MMIO_MITIGATION_VERW) {
/*
* Check if the system has the right microcode.
*
* CPU Fill buffer clear mitigation is enumerated by either an explicit
* FB_CLEAR or by the presence of both MD_CLEAR and L1D_FLUSH on MDS
* affected systems.
*/
if (!((x86_arch_cap_msr & ARCH_CAP_FB_CLEAR) ||
(boot_cpu_has(X86_FEATURE_MD_CLEAR) &&
boot_cpu_has(X86_FEATURE_FLUSH_L1D) &&
!(x86_arch_cap_msr & ARCH_CAP_MDS_NO))))
mmio_mitigation = MMIO_MITIGATION_UCODE_NEEDED;
}
pr_info("%s\n", mmio_strings[mmio_mitigation]);
}
static void __init mmio_apply_mitigation(void)
{
if (mmio_mitigation == MMIO_MITIGATION_OFF)
return;
/*
* X86_FEATURE_CLEAR_CPU_BUF could be enabled by other VERW based
* mitigations, disable KVM-only mitigation in that case.
* Only enable the VMM mitigation if the CPU buffer clear mitigation is
* not being used.
*/
if (boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
if (verw_clear_cpu_buf_mitigation_selected) {
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
static_branch_disable(&cpu_buf_vm_clear);
else
} else {
static_branch_enable(&cpu_buf_vm_clear);
}
/*
* If Processor-MMIO-Stale-Data bug is present and Fill Buffer data can
@@ -548,21 +590,6 @@ static void __init mmio_select_mitigation(void)
if (!(x86_arch_cap_msr & ARCH_CAP_FBSDP_NO))
static_branch_enable(&mds_idle_clear);
/*
* Check if the system has the right microcode.
*
* CPU Fill buffer clear mitigation is enumerated by either an explicit
* FB_CLEAR or by the presence of both MD_CLEAR and L1D_FLUSH on MDS
* affected systems.
*/
if ((x86_arch_cap_msr & ARCH_CAP_FB_CLEAR) ||
(boot_cpu_has(X86_FEATURE_MD_CLEAR) &&
boot_cpu_has(X86_FEATURE_FLUSH_L1D) &&
!(x86_arch_cap_msr & ARCH_CAP_MDS_NO)))
mmio_mitigation = MMIO_MITIGATION_VERW;
else
mmio_mitigation = MMIO_MITIGATION_UCODE_NEEDED;
if (mmio_nosmt || cpu_mitigations_auto_nosmt())
cpu_smt_disable(false);
}
@@ -685,7 +712,6 @@ static void __init md_clear_update_mitigation(void)
static void __init md_clear_select_mitigation(void)
{
mmio_select_mitigation();
rfds_select_mitigation();
/*