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Tue, 12 Nov 2024 13:19:21 -0800 (PST) From: Andrew Cooper To: Xen-devel Cc: Andrew Cooper , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , Stefano Stabellini Subject: [PATCH v2 2/3] x86/ucode: Fix cache handling in microcode_update_helper() Date: Tue, 12 Nov 2024 21:19:14 +0000 Message-Id: <20241112211915.1473121-3-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20241112211915.1473121-1-andrew.cooper3@citrix.com> References: <20241112211915.1473121-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @citrix.com) X-ZM-MESSAGEID: 1731446393216116600 microcode_update_cache() now has a single caller, but inlining it shows how unnecessarily complicated the logic really is. Outside of error paths, there is always one microcode patch to free. Its either result of parse_blob(), or it's the old cached value. In order to fix this, have a local patch pointer (mostly to avoid the unnecessary verbosity of patch_with_flags.patch), and always free it at the end. The only error path needing care is the IS_ERR(patch) path, which is easy enough to handle. Also, widen the scope of result. We only need to call compare_patch() once, and the answer is still good later when updating the cache. In order to update the cache, simply SWAP() the patch and the cache pointers, allowing = the singular xfree() at the end to cover both cases. This also removes all callers microcode_free_patch() which fixes the need to cast away const to allow it to compile. This also removed several violatio= ns of MISRA Rule 11.8 which disallows casting away const. No functional change. Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- CC: Jan Beulich CC: Roger Pau Monn=C3=A9 CC: Stefano Stabellini --- xen/arch/x86/cpu/microcode/core.c | 66 +++++++++++-------------------- 1 file changed, 24 insertions(+), 42 deletions(-) diff --git a/xen/arch/x86/cpu/microcode/core.c b/xen/arch/x86/cpu/microcode= /core.c index 5897ec54032a..0cc5daa251e2 100644 --- a/xen/arch/x86/cpu/microcode/core.c +++ b/xen/arch/x86/cpu/microcode/core.c @@ -86,7 +86,7 @@ struct patch_with_flags { static bool ucode_in_nmi =3D true; =20 /* Protected by microcode_mutex */ -static const struct microcode_patch *microcode_cache; +static struct microcode_patch *microcode_cache; =20 /* * opt_mod_idx and opt_scan have subtle semantics. @@ -192,33 +192,6 @@ static struct microcode_patch *parse_blob(const char *= buf, size_t len) return alternative_call(ucode_ops.cpu_request_microcode, buf, len, tru= e); } =20 -static void microcode_free_patch(const struct microcode_patch *patch) -{ - xfree((struct microcode_patch *)patch); -} - -/* Return true if cache gets updated. Otherwise, return false */ -static bool microcode_update_cache(const struct microcode_patch *patch) -{ - ASSERT(spin_is_locked(µcode_mutex)); - - if ( !microcode_cache ) - microcode_cache =3D patch; - else if ( alternative_call(ucode_ops.compare_patch, - patch, microcode_cache) =3D=3D NEW_UCODE ) - { - microcode_free_patch(microcode_cache); - microcode_cache =3D patch; - } - else - { - microcode_free_patch(patch); - return false; - } - - return true; -} - /* Returns true if ucode should be loaded on a given cpu */ static bool is_cpu_primary(unsigned int cpu) { @@ -496,6 +469,8 @@ struct ucode_buf { =20 static long cf_check microcode_update_helper(void *data) { + struct microcode_patch *patch =3D NULL; + enum microcode_match_result result; int ret; struct ucode_buf *buffer =3D data; unsigned int cpu, updated; @@ -524,17 +499,20 @@ static long cf_check microcode_update_helper(void *da= ta) goto put; } =20 - patch_with_flags.patch =3D parse_blob(buffer->buffer, buffer->len); + patch =3D parse_blob(buffer->buffer, buffer->len); patch_with_flags.flags =3D buffer->flags; + xfree(buffer); - if ( IS_ERR(patch_with_flags.patch) ) + + if ( IS_ERR(patch) ) { - ret =3D PTR_ERR(patch_with_flags.patch); + ret =3D PTR_ERR(patch); + patch =3D NULL; printk(XENLOG_WARNING "Parsing microcode blob error %d\n", ret); goto put; } =20 - if ( !patch_with_flags.patch ) + if ( !patch ) { printk(XENLOG_WARNING "microcode: couldn't find any matching ucode= in " "the provided blob!\n"); @@ -549,10 +527,7 @@ static long cf_check microcode_update_helper(void *dat= a) spin_lock(µcode_mutex); if ( microcode_cache ) { - enum microcode_match_result result; - - result =3D alternative_call(ucode_ops.compare_patch, - patch_with_flags.patch, microcode_cache); + result =3D alternative_call(ucode_ops.compare_patch, patch, microc= ode_cache); =20 if ( result !=3D NEW_UCODE && !(ucode_force && (result =3D=3D OLD_UCODE || result =3D=3D SA= ME_UCODE)) ) @@ -561,12 +536,13 @@ static long cf_check microcode_update_helper(void *da= ta) printk(XENLOG_WARNING "microcode: couldn't find any newer%s revision in the p= rovided blob!\n", ucode_force ? " (or a valid)" : ""); - microcode_free_patch(patch_with_flags.patch); ret =3D -EEXIST; =20 goto put; } } + else + result =3D NEW_UCODE; spin_unlock(µcode_mutex); =20 cpumask_clear(&cpu_callin_map); @@ -593,14 +569,18 @@ static long cf_check microcode_update_helper(void *da= ta) * this requirement can be relaxed in the future. Right now, this is * conservative and good. */ + patch_with_flags.patch =3D patch; ret =3D stop_machine_run(do_microcode_update, &patch_with_flags, NR_CP= US); =20 updated =3D atomic_read(&cpu_updated); if ( updated > 0 ) { - spin_lock(µcode_mutex); - microcode_update_cache(patch_with_flags.patch); - spin_unlock(µcode_mutex); + if ( result =3D=3D NEW_UCODE ) + { + spin_lock(µcode_mutex); + SWAP(patch, microcode_cache); + spin_unlock(µcode_mutex); + } =20 /* * Refresh the raw CPU policy, in case the features have changed. @@ -615,8 +595,6 @@ static long cf_check microcode_update_helper(void *data) if ( ctxt_switch_masking ) alternative_vcall(ctxt_switch_masking, current); } - else - microcode_free_patch(patch_with_flags.patch); =20 if ( updated && updated !=3D nr_cores ) printk(XENLOG_ERR "ERROR: Updating microcode succeeded on %u cores= and failed\n" @@ -627,6 +605,10 @@ static long cf_check microcode_update_helper(void *dat= a) =20 put: put_cpu_maps(); + + /* The parsed blob or old cached value, whichever we're not keeping. */ + xfree(patch); + return ret; } =20 --=20 2.39.5