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Fri, 26 Sep 2025 05:00:05 -0700 (PDT) Message-ID: <5472d09f-4bce-4aeb-b517-79348923281d@suse.com> Date: Fri, 26 Sep 2025 14:00:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [XEN][PATCH] x86/hvm: vlapic: fix RO bits emulation in LVTx regs To: Grygorii Strashko Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Alejandro Vallejo , Jason Andryuk , "xen-devel@lists.xenproject.org" References: <20250925195558.519568-1-grygorii_strashko@epam.com> <67dd3659-916b-4e64-afe2-e13fdc8d31f0@suse.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 26.09.2025 13:34, Grygorii Strashko wrote: > On 26.09.25 13:52, Jan Beulich wrote: >> On 26.09.2025 12:38, Grygorii Strashko wrote: >>> On 26.09.25 11:17, Jan Beulich wrote: >>>> On 25.09.2025 21:55, Grygorii Strashko wrote: >>>> While looking at this, don't we have an issue with CMCI as well? >>> >>> I see no APIC_CMCI write emulation. only read. >> >> guest_wrmsr_x2apic() has >> >> case APIC_CMCI: > > it will end up calling vlapic_reg_write() which doesn't have case statement for > APIC_CMCI - write ignored. Which again is what I had described. >>>> guest_{rd,wr}msr_x2apic() handle it, but vlapic_reg_write() doesn't. I.e. on >>>> AMD we would fail to deliver #GP when the guest accesses it, while on Intel >>>> we would lose the value written. And we also don't set its mask bit in >>>> vlapic_do_init(). I guess I need to make a patch ... >>> >>> Is'n it depends on CMCI capability exposing to guest? >> >> Yes, that's part of what I was (effectively) saying. >> >>> (have no idea what's CMCI :) >> >> Corrected Machine Check Interrupt. > > Looking at: > > #define VLAPIC_VERSION 0x00050014 > > which means "Max LVT Entries" = 6 (5+1) > > Looking at linux kernel apic.c: > #ifdef CONFIG_X86_MCE_INTEL > if (maxlvt >= 6) { > v = apic_read(APIC_LVTCMCI); > if (!(v & APIC_LVT_MASKED)) > apic_write(APIC_LVTCMCI, v | APIC_LVT_MASKED); > } > #endif > > Which means Xen never really emulated APIC_CMCI, so wouldn't it be correct to just drop APIC_CMCI? >From the SDM it's not quite clear to me whether using the LVT count is the correct / only way to determine whether there's a CMCI LVT entry. To me it reads more like the MCG_CAP bit is what is the basis. Perhaps based on that we should conditionally set the LVT count to 6 (AMD) or 7 (Intel). > Also, taking into account that it's Intel specific. Another part of what I said I think needs correcting. Jan